| **Allowance for Loan Losses - Risk Ratings by Segment (Details) - USD ($) $ in Thousands** | Dec. 31, 2016 | Dec. 31, 2015 |
|--------------------------------------------------------------------------------------------|---------------|---------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | $ 505,737     | $ 442,435     |
| Commercial | Real Estate                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 302,506       | 269,462       |
| Commercial | Construction                                                                  |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 25,406        | 24,881        |
| Commercial | Other                                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 150,769       | 128,341       |
| Municipal                                                                                  |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 27,056        | 19,751        |
| 1 Strong                                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 852           | 1,262         |
| 1 Strong | Commercial | Real Estate                                                        |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 2             | 6             |
| 1 Strong | Commercial | Construction                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 1 Strong | Commercial | Other                                                              |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 850           | 1,256         |
| 1 Strong | Municipal                                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 2 Above average                                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 48,491        | 55,059        |
| 2 Above average | Commercial | Real Estate                                                 |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 13,981        | 29,176        |
| 2 Above average | Commercial | Construction                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 49            | 56            |
| 2 Above average | Commercial | Other                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 8,934         | 7,506         |
| 2 Above average | Municipal                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 25,527        | 18,321        |
| 3 Satisfactory                                                                             |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 132,372       | 85,095        |
| 3 Satisfactory | Commercial | Real Estate                                                  |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 81,286        | 52,821        |
| 3 Satisfactory | Commercial | Construction                                                 |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 1,345         | 2,057         |
| 3 Satisfactory | Commercial | Other                                                        |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 48,212        | 28,787        |
| 3 Satisfactory | Municipal                                                                 |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 1,529         | 1,430         |
| 4 Average                                                                                  |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 221,073       | 207,442       |
| 4 Average | Commercial | Real Estate                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 139,421       | 122,071       |
| 4 Average | Commercial | Construction                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 16,506        | 18,070        |
| 4 Average | Commercial | Other                                                             |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 65,146        | 67,301        |
| 4 Average | Municipal                                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 5 Watch                                                                                    |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 67,394        | 58,700        |
| 5 Watch | Commercial | Real Estate                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 43,181        | 36,075        |
| 5 Watch | Commercial | Construction                                                        |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 7,349         | 4,490         |
| 5 Watch | Commercial | Other                                                               |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 16,864        | 18,135        |
| 5 Watch | Municipal                                                                        |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 6 OAEM                                                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 6,156         | 12,152        |
| 6 OAEM | Commercial | Real Estate                                                          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 4,569         | 9,742         |
| 6 OAEM | Commercial | Construction                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 6 OAEM | Commercial | Other                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 1,587         | 2,410         |
| 6 OAEM | Municipal                                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 8 Doubtful                                                                                 |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 29,399        | 22,725        |
| 8 Doubtful | Commercial | Real Estate                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 20,066        | 19,571        |
| 8 Doubtful | Commercial | Construction                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 157           | 208           |
| 8 Doubtful | Commercial | Other                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 9,176         | 2,946         |
| 8 Doubtful | Municipal                                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 8 Doubtful                                                                                 |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 8 Doubtful | Commercial | Real Estate                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 8 Doubtful | Commercial | Construction                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 8 Doubtful | Commercial | Other                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | 0             | 0             |
| 8 Doubtful | Municipal                                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                           |          |          |
| Risk rated loans receivable                                                                | $ 0           | $ 0           |

| X                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans subject to review and validation annually by independent consulting firm as well internal credit review function.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=fnlc_MunicipalPortfolioMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=fnlc_Strong1Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=fnlc_AboveAverage2Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
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| X                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=fnlc_Average4Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=fnlc_Watch5Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=fnlc_Oaem6Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
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| X                                                                                                                                                   |
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