| **Investment Securities Amortized Cost and Estimated Fair Value of Held to Maturity Securities (Details) (USD $)In Thousands, unless otherwise specified** | Jun. 30, 2014 | Dec. 31, 2013 | Jun. 30, 2013 |
|------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                                                   |          |          |          |
| Amortized Cost                                                                                                                                             | $ 198,135     | $ 169,277     | $ 177,264     |
| Unrealized Gains                                                                                                                                           | 4,315         | 3,264         | 4,161         |
| Unrealized Losses                                                                                                                                          | (6,900)       | (14,205)      | (6,635)       |
| Fair Value (Estimated)                                                                                                                                     | 195,550       | 158,336       | 174,790       |
| US Treasury and Government [Member]                                                                                                                        |          |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                                                   |          |          |          |
| Amortized Cost                                                                                                                                             | 92,324        | 92,280        | 92,179        |
| Unrealized Gains                                                                                                                                           | 5             | 1             | 10            |
| Unrealized Losses                                                                                                                                          | (6,343)       | (12,757)      | (5,944)       |
| Fair Value (Estimated)                                                                                                                                     | 85,986        | 79,524        | 86,245        |
| Collateralized Mortgage Backed Securities [Member]                                                                                                         |          |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                                                   |          |          |          |
| Amortized Cost                                                                                                                                             | 65,835        | 35,712        | 42,389        |
| Unrealized Gains                                                                                                                                           | 1,851         | 1,440         | 1,883         |
| Unrealized Losses                                                                                                                                          | (526)         | (1,336)       | (625)         |
| Fair Value (Estimated)                                                                                                                                     | 67,160        | 35,816        | 43,647        |
| US States and Political Subdivisions Debt Securities [Member]                                                                                              |          |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                                                   |          |          |          |
| Amortized Cost                                                                                                                                             | 39,676        | 40,985        | 42,396        |
| Unrealized Gains                                                                                                                                           | 2,459         | 1,823         | 2,268         |
| Unrealized Losses                                                                                                                                          | (31)          | (112)         | (66)          |
| Fair Value (Estimated)                                                                                                                                     | 42,104        | 42,696        | 44,598        |
| Corporate Debt Securities [Member]                                                                                                                         |          |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                                                   |          |          |          |
| Amortized Cost                                                                                                                                             | 300           | 300           | 300           |
| Unrealized Gains                                                                                                                                           | 0             | 0             | 0             |
| Unrealized Losses                                                                                                                                          | 0             | 0             | 0             |
| Fair Value (Estimated)                                                                                                                                     | $ 300         | $ 300         | $ 300         |

| X                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.
+ References
No definition available.
+ Details**Name:**fnlc_HeldtomaturitySecuritiesAccumulatedUnrecognizedHoldingGain**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.
+ References
No definition available.
+ Details**Name:**fnlc_HeldtomaturitySecuritiesAccumulatedUnrecognizedHoldingLoss**Namespace Prefix:**fnlc_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.
+ References
No definition available.
+ Details**Name:**us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of investments in debt securities classified as held-to-maturity.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563
+ Details**Name:**us-gaap_HeldToMaturitySecuritiesFairValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |