| **Allowance for Loan Losses TDR's by Class of Loan and the Associated Specific Reserve (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended | 6 Months Ended |
|----------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 3              | 15             | 10 | 29 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | $ 936          | $ 5,105        | $ 3,890 | $ 8,107 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 783            | 4,955          | 3,724 | 7,919 |
| Specific Reserves                                                                                                                                  | 0              | 1,454          | 0 | 1,468 |
| Commercial Real Estate Portfolio Segment [Member]                                                                                                  |           |           |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 0              | 5              | 2 | 12 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | 0              | 1,598          | 1,897 | 4,032 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 0              | 1,449          | 1,897 | 3,845 |
| Specific Reserves                                                                                                                                  | 0              | 152            | 0 | 152 |
| Commercial Construction [Member]                                                                                                                   |           |           |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 0              | 1              | 0 | 1 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | 0              | 1,951          | 0 | 1,951 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 0              | 1,951          | 0 | 1,951 |
| Specific Reserves                                                                                                                                  | 0              | 696            | 0 | 696 |
| Commercial Other [Member]                                                                                                                          |           |           |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 2              | 6              | 5 | 9 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | 623            | 701            | 1,164 | 713 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 620            | 700            | 1,150 | 712 |
| Specific Reserves                                                                                                                                  | 0              | 545            | 0 | 544 |
| Municipal [Member]                                                                                                                                 |           |           |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 0              | 0              | 0 | 0 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | 0              | 0              | 0 | 0 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 0              | 0              | 0 | 0 |
| Specific Reserves                                                                                                                                  | 0              | 0              | 0 | 0 |
| Residential Term [Member]                                                                                                                          |           |           |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 1              | 3              | 2 | 7 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | 313            | 855            | 625 | 1,411 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 163            | 855            | 475 | 1,411 |
| Specific Reserves                                                                                                                                  | 0              | 61             | 0 | 76 |
| Home Equity [Member]                                                                                                                               |           |           |   |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                                   |           |           |   |   |
| Number of Loans                                                                                                                                    | 0              | 0              | 1 | 0 |
| Pre-Modification Outstanding Recorded Investment                                                                                                   | 0              | 0              | 204 | 0 |
| Post-Modification Outstanding Recorded Investment                                                                                                  | 0              | 0              | 202 | 0 |
| Specific Reserves                                                                                                                                  | $ 0            | $ 0            | $ 0 | $ 0 |

| 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 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
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                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |