| **Loans - TDRs by Class and Specific Reserve (Details) $ in Thousands** | 12 Months Ended |
|-------------------------------------------------------------------------|-----------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 71              | 84 |
| Balance                                                                 | $ 21,526        | $ 23,923 |
| Specific Reserves                                                       | $ 736           | $ 455 |
| Commercial | Real Estate                                                |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 10              | 15 |
| Balance                                                                 | $ 8,937         | $ 10,350 |
| Specific Reserves                                                       | $ 375           | $ 85 |
| Commercial | Construction                                               |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 1               | 1 |
| Balance                                                                 | $ 763           | $ 788 |
| Specific Reserves                                                       | $ 100           | $ 94 |
| Commercial | Other                                                      |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 5               | 11 |
| Balance                                                                 | $ 779           | $ 1,168 |
| Specific Reserves                                                       | $ 0             | $ 1 |
| Municipal                                                               |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 0               | 0 |
| Balance                                                                 | $ 0             | $ 0 |
| Specific Reserves                                                       | $ 0             | $ 0 |
| Residential | Construction                                              |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 0               | 0 |
| Balance                                                                 | $ 0             | $ 0 |
| Specific Reserves                                                       | $ 0             | $ 0 |
| Residential | Term                                                      |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 52              | 53 |
| Balance                                                                 | $ 10,503        | $ 10,875 |
| Specific Reserves                                                       | $ 261           | $ 275 |
| Home Equity LIne of Credit                                              |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 3               | 4 |
| Balance                                                                 | $ 544           | $ 742 |
| Specific Reserves                                                       | $ 0             | $ 0 |
| Consumer                                                                |            |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |            |   |
| Number of Loans | loan                                                  | 0               | 0 |
| Balance                                                                 | $ 0             | $ 0 |
| Specific Reserves                                                       | $ 0             | $ 0 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Specific allowance for loan and lease losses on receivable financings that are classified as troubled debt restructurings during the period.
+ References
No definition available.
+ Details**Name:**fnlc_TroubledDebtRestructuringLoansAndLeasesReceivableSpecificAllowanceDuringPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| 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
Number of financing receivables that have been 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_FinancingReceivableModificationsNumberOfContracts2**Namespace Prefix:**us-gaap_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Recorded Investment -URI http://asc.fasb.org/extlink&oid=65880944
+ Details**Name:**us-gaap_FinancingReceivableModificationsRecordedInvestment**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**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:** |