| **Loans - TDR's by Class and Associated Specific Reserves (Details) $ in Thousands** | 12 Months Ended |
|--------------------------------------------------------------------------------------|-----------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 12              | 8 |
| Balance                                                                              | $ 2,303         | $ 1,053 |
| Specific Reserves                                                                    | $ 290           | $ 46 |
| Number of Loans | loan                                                               | 0               | 2 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 221 |
| Post-Modification Outstanding Recorded Investment                                    |            | 218 |
| Specific Reserves                                                                    |            | $ 0 |
| Commercial | Real Estate                                                             |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 1               | 0 |
| Balance                                                                              | $ 822           | $ 0 |
| Specific Reserves                                                                    | $ 264           | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |
| Commercial | Construction                                                            |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 0               | 0 |
| Balance                                                                              | $ 0             | $ 0 |
| Specific Reserves                                                                    | $ 0             | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |
| Commercial | Other                                                                   |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 0               | 0 |
| Balance                                                                              | $ 0             | $ 0 |
| Specific Reserves                                                                    | $ 0             | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |
| Municipal                                                                            |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 0               | 0 |
| Balance                                                                              | $ 0             | $ 0 |
| Specific Reserves                                                                    | $ 0             | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |
| Residential | Construction                                                           |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 0               | 0 |
| Balance                                                                              | $ 0             | $ 0 |
| Specific Reserves                                                                    | $ 0             | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |
| Residential | Term                                                                   |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 10              | 8 |
| Balance                                                                              | $ 1,314         | $ 1,053 |
| Specific Reserves                                                                    | $ 26            | $ 46 |
| Number of Loans | loan                                                               |            | 2 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 221 |
| Post-Modification Outstanding Recorded Investment                                    |            | 218 |
| Specific Reserves                                                                    |            | $ 0 |
| Home Equity LIne of Credit                                                           |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 1               | 0 |
| Balance                                                                              | $ 167           | $ 0 |
| Specific Reserves                                                                    | $ 0             | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |
| Consumer                                                                             |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                     |            |   |
| Number of Loans | loan                                                               | 0               | 0 |
| Balance                                                                              | $ 0             | $ 0 |
| Specific Reserves                                                                    | $ 0             | $ 0 |
| Number of Loans | loan                                                               |            | 0 |
| Pre-Modification Outstanding Recorded Investment                                     |            | $ 0 |
| Post-Modification Outstanding Recorded Investment                                    |            | 0 |
| Specific Reserves                                                                    |            | $ 0 |

| X                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of financing receivables that have been modified by troubled debt restructurings during the current period.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableModificationsNumberOfContractsDuringPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of financing receivables greater than 30 days past due that have been modified by troubled debt restructurings and that have been placed in the TDR status in the previous 12 months.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableModificationsNumberOfContractsGreaterThan30DaysPastDuePlaceInTDRInPrevious12Months**Namespace Prefix:**fnlc_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivables that are greater than 30 days past due and that had been placed in TDR status in the previous 12 months.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableRecordedInvestmentGreaterThan30DaysPastDuePlacedInTDRInPrevious12Months**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing Receivable, Recorded Investment, Greater than 30 Days Past Due, Placed in T D R in Previous 12 months, Specific Allowance during Period
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableRecordedInvestmentGreaterthan30DaysPastDuePlacedinTDRinPrevious12monthsSpecificAllowanceduringPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Specific allowance for loan and lease losses on receivable financings that are classified as troubled debt restructurings during the current period.
+ References
No definition available.
+ Details**Name:**fnlc_TroubledDebtRestructuringLoansAndLeasesReceivableSpecificAllowanceCurrentPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Post-modification amount of investment in financing receivables modified by troubled debt restructurings.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524
+ Details**Name:**us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524
+ Details**Name:**us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fnlc_OtherLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=fnlc_MunicipalPortfolioMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fnlc_TermLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=fnlc_HomeEquityLIneofCreditPortfolioMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |