| **Loans TDR's by Class and the Associated Specific Reserves (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended | 6 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 3              | 3              | 10 |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 12             | 12             | 12 |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              | $ 2,197        | $ 2,052        | $ 2,197 |
| Days Past Due Placed In T D R In Previous12 Months                                                                      | 20             | 315            | 20 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 936            | 349            | 3,890 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 783            | 291            | 3,724 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 17             | 0 |
| Consumer Portfolio Segment [Member]                                                                                     |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    |           | 0              | 0 |
| Residential Construction [Member]                                                                                       |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    |           | 0              | 0 |
| Commercial Real Estate Portfolio Segment [Member]                                                                       |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 0              | 0              | 2 |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              | 319            | 518            | 319 |
| Days Past Due Placed In T D R In Previous12 Months                                                                      | 5              | 259            | 5 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 0              | 0              | 1,897 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 0              | 0              | 1,897 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 0              | 0 |
| Commercial Construction [Member]                                                                                        |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 0              | 0              | 0 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 0              | 0              | 0 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 0              | 0              | 0 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 0              | 0 |
| Commercial Real Estate Other Receivable [Member]                                                                        |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    |           | 0              | 5 |
| Commercial Other [Member]                                                                                               |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 2              |           |   |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              | 370            | 0              | 370 |
| Days Past Due Placed In T D R In Previous12 Months                                                                      | 9              | 0              | 9 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 623            | 0              | 1,164 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 620            | 0              | 1,150 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 0              | 0 |
| Municipal [Member]                                                                                                      |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 0              | 0              | 0 |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 0              | 0              | 0 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 0              | 0              | 0 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 0              | 0              | 0 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 0              | 0 |
| Residential Term [Member]                                                                                               |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 1              | 3              | 2 |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              | 1,085          | 1,333          | 1,085 |
| Days Past Due Placed In T D R In Previous12 Months                                                                      | 6              | 35             | 6 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 313            | 349            | 625 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 163            | 291            | 475 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 17             | 0 |
| Home Equity [Member]                                                                                                    |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts During Period                                                    | 0              | 0              | 1 |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              | 0              |           | 0 |
| Days Past Due Placed In T D R In Previous12 Months                                                                      | 0              |           | 0 |
| Financing Receivable Modifications Pre Modification Recorded Investment During Period                                   | 0              | 0              | 204 |
| Financing Receivable Modifications Post Modification Recorded Investment During Period                                  | 0              | 0              | 202 |
| Troubled Debt Restructuring, Loans and Leases Receivable, Specific Allowance Current Period                             | 0              | 0              | 0 |
| Commercial Real Estate [Member]                                                                                         |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 2              | 1              | 2 |
| Consumer Loan [Member]                                                                                                  |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 0              | 0              | 0 |
| Residential Construction [Member]                                                                                       |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 0              | 0              | 0 |
| Commercial Real Estate Construction Financing Receivable [Member]                                                       |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 1              | 0              | 1 |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              | 423            |           | 423 |
| Residential Term [Member]                                                                                               |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 7              | 10             | 7 |
| Home Equity [Member]                                                                                                    |           |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                        |           |           |   |
| Financing Receivable Modifications Number Of Contracts Greater Than30 Days Past Due Place In T D R In Previous12 Months | 0              | 1              | 0 |
| Financing Receivable Recorded Investment Greater Than30 Days Past Due Placed In T D R In Previous12 Months              |           | 201            |   |
| Days Past Due Placed In T D R In Previous12 Months                                                                      |           | $ 21           |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Specific allowance for loan and lease losses on receivable financings greater 30 days past due that are classified as troubled debt restructurings during the period and that had been placed in TDR status in the previous 12 months.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of financing receivables that have been modified by troubled debt restructurings during the current period.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableModificationsNumberOfContractsDuringPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of financing receivables greater than 30 days past due that have been modified by troubled debt restructurings and that have been placed in the TDR status in the previous 12 months.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableModificationsNumberOfContractsGreaterThan30DaysPastDuePlaceInTDRInPrevious12Months**Namespace Prefix:**fnlc_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings after the financing receivable has been modified during the current period.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableModificationsPostModificationRecordedInvestmentDuringPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings before the financing receivable has been modified during the current period.
+ References
No definition available.
+ Details**Name:**fnlc_FinancingReceivableModificationsPreModificationRecordedInvestmentDuringPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivables that are greater than 30 days past due and that had been placed in TDR status in the previous 12 months.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Specific allowance for loan and lease losses on receivable financings that are classified as troubled debt restructurings during the current period.
+ References
No definition available.
+ Details**Name:**fnlc_TroubledDebtRestructuringLoansAndLeasesReceivableSpecificAllowanceCurrentPeriod**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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