| **Other Comprehensive Income (Loss) - Reclassification of Available-for-Sale Securities to Held-to-Maturity Securities (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------|
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| **Reclassification of Available-for-Sale Securities to Held-to-maturity Roll Forward [Roll Forward]**                                                                              |                                                                                                                          |   |
| Balance at beginning of period                                                                                                                                                     | $ (48)fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity    | $ 0fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity |
| Net unrealized losses transferred during the period                                                                                                                                | 0fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtomaturitybeforeTax                            | 0fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtomaturitybeforeTax |
| Amortization of net unrealized losses                                                                                                                                              | (14)fnlc_OtherComprehensiveIncomeLossAmortizationofNetUnrealizedLossesonTransfersofAvailableforSalesecuritiestoHeldtoMaturity | 0fnlc_OtherComprehensiveIncomeLossAmortizationofNetUnrealizedLossesonTransfersofAvailableforSalesecuritiestoHeldtoMaturity |
| Related deferred taxes                                                                                                                                                             | (5)fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtoMaturityTax                                | 0fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtoMaturityTax |
| Net change                                                                                                                                                                         | (19)fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtomaturityNetofTax                          | 0fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtomaturityNetofTax |
| Balance at end of period                                                                                                                                                           | $ (67)fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity    | $ 0fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Accumulated Unrealized Gain (Loss) on Transfer of Available-for-sale Securities to Held-to-maturity
+ References
No definition available.
+ Details**Name:**fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Amortization of Net Unrealized Losses on Transfers of Available-for-Sale securities to Held-to-Maturity
+ References
No definition available.
+ Details**Name:**fnlc_OtherComprehensiveIncomeLossAmortizationofNetUnrealizedLossesonTransfersofAvailableforSalesecuritiestoHeldtoMaturity**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Transfers from Available-for-Sale Securities to Held-to-maturity, before Tax
+ References
No definition available.
+ Details**Name:**fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtomaturitybeforeTax**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Transfers from Available-for-Sale Securities to Held-to-maturity, Net of Tax
+ References
No definition available.
+ Details**Name:**fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtomaturityNetofTax**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Transfers from Available-for-Sale Securities to Held-to-Maturity, Tax
+ References
No definition available.
+ Details**Name:**fnlc_OtherComprehensiveIncomeLossTransfersfromAvailableforSaleSecuritiestoHeldtoMaturityTax**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**fnlc_ReclassificationofAvailableforSaleSecuritiestoHeldtomaturityRollForwardRollForward**Namespace Prefix:**fnlc_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |