| **Allowance for Loan Losses - Composition of Allowance for Loans Losses, by Class (Details) - USD ($) $ in Thousands** | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 |
|------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|---------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | $ 974         | $ 754         | $ 1,803       |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 9,164         | 9,162         | 8,541         |          |
| Total Allowance for Loan Losses                                                                                        | 10,138        | 9,916         | 10,344        | $ 11,514      |
| Commercial | Real Estate                                                                                               |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 505           | 89            | 346           |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 3,483         | 3,031         | 3,186         |          |
| Total Allowance for Loan Losses                                                                                        | 3,988         | 3,120         | 3,532         | 4,602         |
| Commercial | Construction                                                                                              |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 100           | 302           | 413           |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 296           | 278           | 410           |          |
| Total Allowance for Loan Losses                                                                                        | 396           | 580           | 823           | 575           |
| Commercial | Other                                                                                                     |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 39            | 8             | 129           |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 1,741         | 1,444         | 1,376         |          |
| Total Allowance for Loan Losses                                                                                        | 1,780         | 1,452         | 1,505         | 2,276         |
| Municipal                                                                                                              |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 0             | 0             | 0             |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 18            | 17            | 15            |          |
| Total Allowance for Loan Losses                                                                                        | 18            | 17            | 15            | 15            |
| Residential | Construction                                                                                             |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 0             | 0             | 0             |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 44            | 24            | 20            |          |
| Total Allowance for Loan Losses                                                                                        | 44            | 24            | 20            | 21            |
| Residential | Term                                                                                                     |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 304           | 326           | 519           |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 984           | 1,065         | 666           |          |
| Total Allowance for Loan Losses                                                                                        | 1,288         | 1,391         | 1,185         | 1,099         |
| Home Equity LIne of Credit                                                                                             |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 26            | 29            | 396           |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 781           | 864           | 664           |          |
| Total Allowance for Loan Losses                                                                                        | 807           | 893           | 1,060         | 675           |
| Consumer                                                                                                               |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 0             | 0             | 0             |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 559           | 566           | 542           |          |
| Total Allowance for Loan Losses                                                                                        | 559           | 566           | 542           | 573           |
| Unallocated                                                                                                            |          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                       |          |          |          |          |
| Allowance for Loans Evaluated Individually for Impairment                                                              | 0             | 0             | 0             |          |
| Allowance for Loans Evaluated Collectively for Impairment                                                              | 1,258         | 1,873         | 1,662         |          |
| Total Allowance for Loan Losses                                                                                        | $ 1,258       | $ 1,873       | $ 1,662       | $ 1,678       |

| 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
The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.
+ References
Reference 1: 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=66008989&loc=SL6953423-111524
+ Details**Name:**us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.
+ References
Reference 1: 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=66008989&loc=SL6953423-111524
+ Details**Name:**us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| 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 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524Reference 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=66008989&loc=SL6953423-111524Reference 3: 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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 6.L.1) -URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707Reference 5: 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=d3e15032-111544
+ Details**Name:**us-gaap_LoansAndLeasesReceivableAllowance**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| 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:** |
| X                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |