| **Allowance for Loan Losses Allowance for Loan Losses Narrative (Details) (USD $)In Thousands, unless otherwise specified** | 6 Months Ended | 12 Months Ended |        |         |        |        |
|-----------------------------------------------------------------------------------------------------------------------------|----------------|-----------------|--------|---------|--------|--------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                            |           |            |   |    |   |   |
| Allowance for Loan and Lease Losses, Related Loans, Percentage                                                              | 0.41%          | 0.40%           |   |    |   |   |
| Allowance for Loan and Lease Losses, Related Loans, Period Increase (Decrease)                                              | $ 170          |            |   |    |   |   |
| Less allowance for loan losses                                                                                              | 11,644         | 11,514          | 11,655 | 12,670  | 12,720 | 12,500 |
| Loan value, lower range                                                                                                     | 75.00%         |            |   |    |   |   |
| Construction loans accrual to company capital                                                                               | 22.50%         |            |   |    |   |   |
| Constructions loan portfolio maximum to company capital                                                                     | 100.00%        |            |   |    |   |   |
| Construction and non owner occupied commercial real estate                                                                  | 78.30%         |            |   |    |   |   |
| Construction And Non Owner Occupied Commercial Real Estate Loans Maximum Loan Portfolio To Company Capital                  | 300.00%        |            |   |    |   |   |
| Outstanding loans and commitments subject by independent consulting firm                                                    | 50.00%         |            |   |    |   |   |
| Residential loans typical loan to value range, high                                                                         | 80.00%         |            |   |    |   |   |
| Collateralized consumer loans to individuals loan to value maximum, lower range                                             | 80.00%         |            |   |    |   |   |
| Collateralized consumer loans to individuals loan to value maximum, higher range                                            | 90.00%         |            |   |    |   |   |
| Consumer Loan [Member]                                                                                                      |           |            |   |    |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                            |           |            |   |    |   |   |
| Delinquent period before residential loans placed on non accrual status                                                     | 120 days       |            |   |    |   |   |
| Residential Construction [Member]                                                                                           |           |            |   |    |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                            |           |            |   |    |   |   |
| Less allowance for loan losses                                                                                              | 23             | 21              | 22     | 9       | 9      | 11     |
| Delinquent period before residential loans placed on non accrual status                                                     | 90 days        |            |   |    |   |   |
| Unallocated Financing Receivables [Member]                                                                                  |           |            |   |    |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                            |           |            |   |    |   |   |
| Less allowance for loan losses                                                                                              | 1,927          | 1,678           | 1,830  | 1,275   | 1,089  | 842    |
| Unallocated Reserves [Member]                                                                                               |           |            |   |    |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                            |           |            |   |    |   |   |
| Less allowance for loan losses                                                                                              | 1,927          | 1,678           |   | 1,275   |   |   |
| Percentage of Total Reserve Allowance accounted for by Loan Loss Allowances                                                 | 17.00%         |            |   |    |   |   |
| Unallocated Reserves [Member] | Unallocated Financing Receivables [Member]                                                  |           |            |   |    |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                            |           |            |   |    |   |   |
| Less allowance for loan losses                                                                                              | $ 1,927        | $ 1,678         |   | $ 1,275 |   |   |

| X                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Allowance for Loan and Lease Losses, Related Loans, Percentage
+ References
No definition available.
+ Details**Name:**fnlc_AllowanceforLoanandLeaseLossesRelatedLoansPercentage**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Allowance for Loan and Lease Losses, Related Loans, Period Increase (Decrease)
+ References
No definition available.
+ Details**Name:**fnlc_AllowanceforLoanandLeaseLossesRelatedLoansPeriodIncreaseDecrease**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The high maximum percentage of loan to value for consumer loans based on purchase price of the collateral.
+ References
No definition available.
+ Details**Name:**fnlc_CollateralizedConsumerLoansToIndividualsLoanToValueMaximumRangeHigh**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The low maximum percentage of loan to value for consumer loans based on purchase price of the collateral.
+ References
No definition available.
+ Details**Name:**fnlc_CollateralizedConsumerLoansToIndividualsLoanToValueMaximumRangeLow**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The regulatory maximum allowed ratio of loan portfolio to Company capital for construction and non-owner-occupied commercial real estate.
+ References
No definition available.
+ Details**Name:**fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansMaximumLoanPortfolioToCompanyCapital**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The actual ratio of loan amount to Company capital for construction and non-owner-occupied commercial real estate.
+ References
No definition available.
+ Details**Name:**fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansPortfolioToCompanyCapital**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The regulatory maximum allowed ratio of loan portfolio to Company capital for construction loans.
+ References
No definition available.
+ Details**Name:**fnlc_ConstructionLoanPortfolioMaximumToCompanyCapital**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The ratio of loan portfolio to Company capital for construction loans .
+ References
No definition available.
+ Details**Name:**fnlc_ConstructionLoansActualLoanPortfolioToCompanyCapital**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The minimum amount of days past due at which residential loans are placed on non-accrual status..
+ References
No definition available.
+ Details**Name:**fnlc_DelinquentPeriodBeforeResidentialLoansPlacedOnNonAccrualStatus**Namespace Prefix:**fnlc_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of loans and commitments subject to review by an independent consulting firm each year.
+ References
No definition available.
+ Details**Name:**fnlc_OutstandingLoansAndCommitmentsSubjectByIndependentConsultingFirm**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Total Reserve Allowance accounted for by Loan Loss Allowances
+ References
No definition available.
+ Details**Name:**fnlc_PercentageofTotalReserveAllowanceaccountedforbyLoanLossAllowances**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The high percentage of loan to value range for residential loans based on current appraisal information.
+ References
No definition available.
+ Details**Name:**fnlc_ResidentialLoansTypicalLoanToValueRangeHigh**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The low percentage of loan to value range for residential loans based on current appraisal information.
+ References
No definition available.
+ Details**Name:**fnlc_ResidentialLoansTypicalLoanToValueRangeLow**Namespace Prefix:**fnlc_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| 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 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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph d -Article 9Reference 3: 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=d3e15032-111544Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section L -Subsection 1
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