| **Mortgage Servicing Rights (Details) - USD ($) $ in Thousands**                                                                                   | 12 Months Ended |
|----------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Transfers and Servicing [Abstract]**                                                                                                             |            |   |   |
| Outstanding principal balance of loans serviced for others                                                                                         | $ 250,083       | $ 223,610 |   |
| Net gain from sale of loans                                                                                                                        | 1,211           | 714 | $ 496 |
| Mortgage servicing rights capitalized                                                                                                              | 554             | 487 |   |
| Amortization of mortgage servicing rights                                                                                                          | 459             | 449 |   |
| Fair value of mortgage servicing rights                                                                                                            | $ 1,696         | 1,915 |   |
| Moving average of weekly prepayment data (in months)                                                                                               | 3 months        |   |   |
| Anticipated loan prepayment rate of servicing assets (in hundredths)                                                                               | 15.00%          |   |   |
| Period used to determine average quarterly discount rate (in years)                                                                                | 10 years        |   |   |
| Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, discount rate adjustment factor (in hundredths) | 3.79%           |   |   |
| **Summary of mortgage servicing rights [Abstract]**                                                                                                |            |   |   |
| Mortgage servicing rights                                                                                                                          | $ 5,901         | 5,747 |   |
| Accumulated amortization                                                                                                                           | (4,680)         | (4,619) |   |
| Impairment reserve                                                                                                                                 | (108)           | (35) |   |
| Mortgage servicing rights, net                                                                                                                     | $ 1,113         | $ 1,093 |   |

| X                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cumulative amount of amortization for mortgage servicing rights that has been recognized in the income statement.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The average quarterly discount rate period used as assumption in evaluating the carrying value of mortgage servicing rights.
+ References
No definition available.
+ Details**Name:**fnlc_Averagequarterlydiscountrate**Namespace Prefix:**fnlc_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gross amount, as of the balance sheet date, of mortgage servicing rights.
+ References
No definition available.
+ Details**Name:**fnlc_MortgageServicingRightsGross**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net amount, as of the balance sheet date, of mortgage servicing rights.
+ References
No definition available.
+ Details**Name:**fnlc_MortgageServicingRightsNet**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The moving average period of weekly prepayment data used as assumption in evaluating the carrying value of mortgage servicing rights.
+ References
No definition available.
+ Details**Name:**fnlc_Movingaverageofweeklyprepaymentdata**Namespace Prefix:**fnlc_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net gain from the sale of loans held for sale.
+ References
No definition available.
+ Details**Name:**fnlc_NetGainFromSaleOfLoans**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A reserve for the amount of expected decrease in the value of mortgage servicing rights which cannot be physically measured.
+ References
No definition available.
+ Details**Name:**fnlc_ReserveForImpairmentOfMortgageServicingRights**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Dollar amount of principal outstanding on loans being serviced for others at the balance sheet date.
+ References
No definition available.
+ Details**Name:**fnlc_ResidentialMortgageLoansServicedForOthersOutstandingPrincipal**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of rate spread added to the ten-year US Treasury rate to derive the discount rate used in the fair value calculation for the loan servicing portfolio.
+ References
No definition available.
+ Details**Name:**fnlc_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRateAdjustmentFactor**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The periodic amortization (in proportion to and over the period of estimated net servicing income or loss) of capitalized servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Estimated rate of prepayments of principal on servicing assets and servicing liabilities.
+ References
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| X                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
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| X                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
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