| **Allowance for Loan Losses  - Financing Receivable and Allowance Element by Class (Details) (USD $)In Thousands, unless otherwise specified** | Mar. 31, 2015                                                                                                                                                                                                                                                                                          | Dec. 31, 2014                                                                                                                                                                                                                                                                                          | Mar. 31, 2014                                                                                                                                                                                                                                                                                            | Dec. 31, 2013                                                                                                                                                                     |
|------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | $ 10,196us-gaap_LoansAndLeasesReceivableAllowance                                                                                                                                                                                                                                                      | $ 10,344us-gaap_LoansAndLeasesReceivableAllowance                                                                                                                                                                                                                                                      | $ 11,655us-gaap_LoansAndLeasesReceivableAllowance                                                                                                                                                                                                                                                        | $ 11,514us-gaap_LoansAndLeasesReceivableAllowance                                                                                                                                 |
| Specific Reserves on Loans Evaluated Individually for Impairment                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,436us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember                                                                                                                                  | 1,803us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember                                                                                                                                  | 2,786us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember                                                                                                                                    |                                                                                                                                                                              |
| General Reserves on Loans Based on Historical Loss Experience                                                                                  |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 3,114us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember                                                                                                                                      | 3,282us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember                                                                                                                                      | 3,530us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember                                                                                                                                        |                                                                                                                                                                              |
| Reserves for Qualitative Factors                                                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 3,805us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember                                                                                                                                                        | 3,597us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember                                                                                                                                                        | 3,509us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember                                                                                                                                                          |                                                                                                                                                                              |
| Unallocated Reserves                                                                                                                           |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,841us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_UnallocatedReservesMember                                                                                                                                                                 | 1,662us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_UnallocatedReservesMember                                                                                                                                                                 | 1,830us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_UnallocatedReservesMember                                                                                                                                                                   |                                                                                                                                                                              |
| Commercial real estate                                                                                                                         |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 3,117us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                                                                      | 3,532us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                                                                      | 4,500us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                                                                        | 4,602us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember |
| Commercial real estate | Specific Reserves on Loans Evaluated Individually for Impairment                                                      |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 248us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember | 346us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember | 1,019us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember |                                                                                                                                                                              |
| Commercial real estate | General Reserves on Loans Based on Historical Loss Experience                                                         |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,094us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember   | 1,444us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember   | 1,707us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember     |                                                                                                                                                                              |
| Commercial real estate | Reserves for Qualitative Factors                                                                                      |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,775us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                     | 1,742us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                     | 1,774us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                       |                                                                                                                                                                              |
| Commercial construction                                                                                                                        |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 807us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                                                                                                                                         | 823us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                                                                                                                                         | 590us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                                                                                                                                           | 575us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                    |
| Commercial construction | Specific Reserves on Loans Evaluated Individually for Impairment                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 396us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                  | 413us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                  | 276us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                    |                                                                                                                                                                              |
| Commercial construction | General Reserves on Loans Based on Historical Loss Experience                                                        |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 157us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                      | 186us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                      | 154us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                        |                                                                                                                                                                              |
| Commercial construction | Reserves for Qualitative Factors                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 254us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                                        | 224us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                                        | 160us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialConstructionMember                                          |                                                                                                                                                                              |
| Commercial other                                                                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,714us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                                                                                                                                              | 1,505us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                                                                                                                                              | 2,241us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                                                                                                                                                | 2,276us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                         |
| Commercial other | Specific Reserves on Loans Evaluated Individually for Impairment                                                            |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 347us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                         | 129us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                         | 834us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                           |                                                                                                                                                                              |
| Commercial other | General Reserves on Loans Based on Historical Loss Experience                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 521us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                             | 624us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                             | 690us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                               |                                                                                                                                                                              |
| Commercial other | Reserves for Qualitative Factors                                                                                            |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 846us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                                               | 752us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                                               | 717us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_CommercialOtherMember                                                 |                                                                                                                                                                              |
| Municipal                                                                                                                                      |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 16us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                                                                                                                                       | 15us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                                                                                                                                       | 15us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                                                                                                                                         | 15us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                  |
| Municipal | Specific Reserves on Loans Evaluated Individually for Impairment                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      |                                                                                                                                                                                                                                                                                                   | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                 | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                   |                                                                                                                                                                              |
| Municipal | General Reserves on Loans Based on Historical Loss Experience                                                                      |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      |                                                                                                                                                                                                                                                                                                   | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                     | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                       |                                                                                                                                                                              |
| Municipal | Reserves for Qualitative Factors                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 16us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                                      | 15us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                                      | 15us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_MunicipalMember                                                        |                                                                                                                                                                              |
| Residential term                                                                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,108us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                                                                                                                                              | 1,185us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                                                                                                                                              | 1,232us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                                                                                                                                                | 1,099us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                         |
| Residential term | Specific Reserves on Loans Evaluated Individually for Impairment                                                            |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 421us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                         | 519us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                         | 574us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                           |                                                                                                                                                                              |
| Residential term | General Reserves on Loans Based on Historical Loss Experience                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 298us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                             | 297us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                             | 303us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                               |                                                                                                                                                                              |
| Residential term | Reserves for Qualitative Factors                                                                                            |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 389us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                                               | 369us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                                               | 355us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialTermMember                                                 |                                                                                                                                                                              |
| Residential construction                                                                                                                       |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 23us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                                                                                                                                         | 20us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                                                                                                                                         | 22us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                                                                                                                                           | 21us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                    |
| Residential construction | Specific Reserves on Loans Evaluated Individually for Impairment                                                    |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                   | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                   | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                     |                                                                                                                                                                              |
| Residential construction | General Reserves on Loans Based on Historical Loss Experience                                                       |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 10us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                      | 9us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                       | 10us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                        |                                                                                                                                                                              |
| Residential construction | Reserves for Qualitative Factors                                                                                    |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 13us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                                        | 11us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                                        | 12us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= fnlc_ResidentialConstructionMember                                          |                                                                                                                                                                              |
| Home equity line of credit                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,044us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                                                                                                                | 1,060us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                                                                                                                | 708us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                                                                                                                    | 675us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                             |
| Home equity line of credit | Specific Reserves on Loans Evaluated Individually for Impairment                                                  |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 24us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                            | 396us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                           | 83us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                              |                                                                                                                                                                              |
| Home equity line of credit | General Reserves on Loans Based on Historical Loss Experience                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 716us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                               | 376us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                               | 343us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                 |                                                                                                                                                                              |
| Home equity line of credit | Reserves for Qualitative Factors                                                                                  |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 304us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                 | 288us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                 | 282us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                   |                                                                                                                                                                              |
| Consumer                                                                                                                                       |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 526us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                                    | 542us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                                    | 517us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                                      | 573us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember               |
| Consumer | Specific Reserves on Loans Evaluated Individually for Impairment                                                                    |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember               | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember               | 0us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_SpecificReservesEvaluatedIndividuallyForImpairmentMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                 |                                                                                                                                                                              |
| Consumer | General Reserves on Loans Based on Historical Loss Experience                                                                       |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 318us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                 | 346us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                 | 323us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                   |                                                                                                                                                                              |
| Consumer | Reserves for Qualitative Factors                                                                                                    |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 208us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                   | 196us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                   | 194us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_ReserveForQualitativeFactorsMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                     |                                                                                                                                                                              |
| Unallocated                                                                                                                                    |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | 1,841us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember                                                                                                                           | 1,662us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember                                                                                                                           | 1,830us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember                                                                                                                             | 1,678us-gaap_LoansAndLeasesReceivableAllowance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember      |
| Unallocated | Unallocated Reserves                                                                                                             |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                               |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                              |
| Allowance for loan losses                                                                                                                      | $ 1,841us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_UnallocatedReservesMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember                                 | $ 1,662us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_UnallocatedReservesMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember                                 | $ 1,830us-gaap_LoansAndLeasesReceivableAllowance/ fnlc_FinancingReceivableInformationByTypeOfReserveAxis= fnlc_UnallocatedReservesMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_UnallocatedFinancingReceivablesMember                                   |                                                                                                                                                                              |

| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section L -Subsection 1
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