| **Acquisitions and Intangible Assets - Additional Information (Details) (USD $)In Thousands, unless otherwise specified** | 0 Months Ended                                                                                                                                                                                                                                  |                                                                                                                       |                          |                                                                                      |
|---------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------|--------------------------|--------------------------------------------------------------------------------------|
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| **Business Acquisition [Line Items]**                                                                                     |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| Goodwill                                                                                                                  |                                                                                                                                                                                                                                            |                                                                                                                  | $ 29,805us-gaap_Goodwill | $ 29,805us-gaap_Goodwill                                                             | $ 29,805us-gaap_Goodwill |
| Bank Acquisition From Camden National Bank                                                                                |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| **Business Acquisition [Line Items]**                                                                                     |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| Deposits and loans acquired                                                                                               | 32,300fnlc_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsDepositsAndLoans/ us-gaap_BusinessAcquisitionAxis= fnlc_BankAcquisitionFromCamdenNationalBankMember                                      |                                                                                                                  |                     |                                                                                 |   |
| Price premium                                                                                                             | 2,553fnlc_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedConsiderationPaidInExcessOfIdentifiableFairValueOfAssetsAndLiabilities/ us-gaap_BusinessAcquisitionAxis= fnlc_BankAcquisitionFromCamdenNationalBankMember |                                                                                                                  |                     |                                                                                 |   |
| Core deposit intangible                                                                                                   | 432fnlc_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFiniteLivedIntangibles/ us-gaap_BusinessAcquisitionAxis= fnlc_BankAcquisitionFromCamdenNationalBankMember                                                   |                                                                                                                  |                     |                                                                                 |   |
| Acquired Finite-lived Intangible Assets, Weighted Average Useful Life                                                     | 10 years                                                                                                                                                                                                                                        |                                                                                                                  |                     |                                                                                 |   |
| Goodwill                                                                                                                  | 2,121us-gaap_Goodwill/ us-gaap_BusinessAcquisitionAxis= fnlc_BankAcquisitionFromCamdenNationalBankMember                                                                                                                                        |                                                                                                                  |                     |                                                                                 |   |
| FNB Bankshares                                                                                                            |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| **Business Acquisition [Line Items]**                                                                                     |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| Goodwill                                                                                                                  |                                                                                                                                                                                                                                            | 27,559us-gaap_Goodwill/ us-gaap_BusinessAcquisitionAxis= fnlc_FnbBanksharesMember                                     |                     |                                                                                 |   |
| Total value of consideration                                                                                              |                                                                                                                                                                                                                                            | 47,955us-gaap_BusinessCombinationConsiderationTransferred1/ us-gaap_BusinessAcquisitionAxis= fnlc_FnbBanksharesMember |                     |                                                                                 |   |
| Acquisition In 2011                                                                                                       |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| **Business Acquisition [Line Items]**                                                                                     |                                                                                                                                                                                                                                            |                                                                                                                  |                     |                                                                                 |   |
| Goodwill                                                                                                                  |                                                                                                                                                                                                                                            |                                                                                                                  |                     | $ 125us-gaap_Goodwill/ us-gaap_BusinessAcquisitionAxis= fnlc_AcquisitionIn2011Member |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Consideration Paid In Excess Of Identifiable Carrying Value Of Assets And Liabilities
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Deposits And Loans
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
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| X                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266
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| X                                                                                                                                                    |
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| X                                                                                                                                                                        |
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| X                                                                                                                                                |
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