| **Investment Securities (Tables)**                                                 | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Investments, Debt and Equity Securities [Abstract]**                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Schedule of Available For Sale, Held-to-Maturity, and Restricted Equity Securities | The following table summarizes the amortized cost and estimated fair value of investment securities at March 31, 2015: AmortizedCost Unrealized Gains Unrealized Losses Fair Value (Estimated)Securities available for sale       Mortgage-backed securities$124,969,000 $2,790,000 $(142,000) $127,617,000State and political subdivisions24,384,000 1,328,000 (114,000) 25,598,000Other equity securities2,997,000 105,000 — 3,102,000 $152,350,000 $4,223,000 $(256,000) $156,317,000Securities to be held to maturity       U.S. Government-sponsored agencies$82,974,000 $108,000 $(912,000) $82,170,000Mortgage-backed securities53,228,000 2,030,000 (116,000) 55,142,000State and political subdivisions125,953,000 3,811,000 (129,000) 129,635,000Corporate securities300,000 — — 300,000 $262,455,000 $5,949,000 $(1,157,000) $267,247,000Restricted equity securities       Federal Home Loan Bank Stock$12,875,000 $— $— $12,875,000Federal Reserve Bank Stock1,037,000 — — 1,037,000 $13,912,000 $— $— $13,912,000The following table summarizes the amortized cost and estimated fair value of investment securities at December 31, 2014: AmortizedCost Unrealized Gains Unrealized Losses Fair Value (Estimated)Securities available for sale       Mortgage-backed securities$149,796,000 $2,637,000 $(578,000) $151,855,000State and political subdivisions29,094,000 1,865,000 (104,000) 30,855,000Other equity securities2,490,000 65,000 (4,000) 2,551,000 $181,380,000 $4,567,000 $(686,000) $185,261,000Securities to be held to maturity       U.S. Government-sponsored agencies$92,341,000 $54,000 $(2,066,000) $90,329,000Mortgage-backed securities57,003,000 1,830,000 (116,000) 58,717,000State and political subdivisions126,275,000 4,114,000 (31,000) 130,358,000Corporate securities300,000 — — 300,000 $275,919,000 $5,998,000 $(2,213,000) $279,704,000Restricted equity securities       Federal Home Loan Bank Stock$12,875,000 $— $— $12,875,000Federal Reserve Bank Stock1,037,000 — — 1,037,000 $13,912,000 $— $— $13,912,000The following table summarizes the amortized cost and estimated fair value of investment securities at March 31, 2014: AmortizedCost Unrealized Gains Unrealized Losses Fair Value (Estimated)Securities available for sale       Mortgage-backed securities$172,909,000 $1,917,000 $(2,711,000) $172,115,000State and political subdivisions133,303,000 2,796,000 (4,784,000) 131,315,000Other equity securities2,207,000 66,000 (3,000) 2,270,000 $308,419,000 $4,779,000 $(7,498,000) $305,700,000Securities to be held to maturity       U.S. Government-sponsored agencies$92,312,000 $2,000 $(9,131,000) $83,183,000Mortgage-backed securities49,805,000 1,652,000 (789,000) 50,668,000State and political subdivisions40,436,000 2,070,000 (95,000) 42,411,000Corporate securities300,000 — — 300,000 $182,853,000 $3,724,000 $(10,015,000) $176,562,000Restricted equity securities       Federal Home Loan Bank Stock$12,875,000 $— $— $12,875,000Federal Reserve Bank Stock1,037,000 — — 1,037,000 $13,912,000 $— $— $13,912,000 |
| Contractual Maturities of Investment Securities                                    | The following table summarizes the contractual maturities of investment securities at March 31, 2015: Securities available for sale Securities to be held to maturity AmortizedCost Fair Value (Estimated) AmortizedCost Fair Value (Estimated)Due in 1 year or less$2,842,000 $2,858,000 $1,873,000 $1,899,000Due in 1 to 5 years14,950,000 15,231,000 12,050,000 12,241,000Due in 5 to 10 years17,746,000 18,110,000 47,898,000 49,930,000Due after 10 years113,815,000 117,016,000 200,634,000 203,177,000Equity securities2,997,000 3,102,000 — — $152,350,000 $156,317,000 $262,455,000 $267,247,000The following table summarizes the contractual maturities of investment securities at December 31, 2014: Securities available for sale Securities to be held to maturity AmortizedCost Fair Value (Estimated) AmortizedCost Fair Value (Estimated)Due in 1 year or less$2,309,000 $2,329,000 $1,693,000 $1,713,000Due in 1 to 5 years15,200,000 15,499,000 8,467,000 8,702,000Due in 5 to 10 years18,547,000 19,124,000 50,629,000 52,717,000Due after 10 years142,834,000 145,758,000 215,130,000 216,572,000Equity securities2,490,000 2,551,000 — — $181,380,000 $185,261,000 $275,919,000 $279,704,000The following table summarizes the contractual maturities of investment securities at March 31, 2014: Securities available for sale Securities to be held to maturity AmortizedCost Fair Value (Estimated) AmortizedCost Fair Value (Estimated)Due in 1 year or less$137,000 $137,000 $265,000 $267,000Due in 1 to 5 years19,747,000 20,052,000 5,951,000 6,266,000Due in 5 to 10 years15,868,000 16,190,000 42,272,000 43,472,000Due after 10 years270,460,000 267,051,000 134,365,000 126,557,000Equity securities2,207,000 2,270,000 — — $308,419,000 $305,700,000 $182,853,000 $176,562,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| Schedule of Securities Gains and Losses                                            | The following table shows securities gains and losses for the three months and quarters ended March 31, 2015 and 2014: For the three months ended March 31, 2015 2014Proceeds from sales of securities$35,465,000 $—Gross realized gains1,395,000 36,000Gross realized losses— —Net gain$1,395,000 $36,000Related income taxes$488,000 $13,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| Schedule of Temporary Impairment Losses                                            | Information regarding securities temporarily impaired as of March 31, 2015 is summarized below: Less than 12 months 12 months or more Total Fair Value (Estimated) Unrealized Losses Fair Value (Estimated) Unrealized Losses Fair Value (Estimated) Unrealized LossesU.S. Government-sponsored agencies$36,459,000 $(595,000) $10,903,000 $(317,000) $47,362,000 $(912,000)Mortgage-backed securities20,634,000 (256,000) 65,000 (2,000) 20,699,000 (258,000)State and political subdivisions10,390,000 (201,000) 1,641,000 (42,000) 12,031,000 (243,000) $67,483,000 $(1,052,000) $12,609,000 $(361,000) $80,092,000 $(1,413,000)As of December 31, 2014, there were 56 securities with unrealized losses held in the Company's portfolio. These securities were temporarily impaired as a result of changes in interest rates reducing their fair value, of which 36 had been temporarily impaired for 12 months or more. Information regarding securities temporarily impaired as of December 31, 2014 is summarized below: Less than 12 months 12 months or more Total Fair Value (Estimated) Unrealized Losses Fair Value (Estimated) Unrealized Losses Fair Value (Estimated) Unrealized LossesU.S. Government-sponsored agencies$— $— $79,444,000 $(2,066,000) $79,444,000 $(2,066,000)Mortgage-backed securities13,878,000 (40,000) 29,182,000 (654,000) 43,060,000 (694,000)State and political subdivisions3,352,000 (31,000) 3,017,000 (104,000) 6,369,000 (135,000)Other equity securities68,000 (3,000) 51,000 (1,000) 119,000 (4,000) $17,298,000 $(74,000) $111,694,000 $(2,825,000) $128,992,000 $(2,899,000)As of March 31, 2014, there were 268 securities with unrealized losses held in the Company's portfolio. These securities were temporarily impaired as a result of changes in interest rates reducing their fair value, of which 73 had been temporarily impaired for 12 months or more. Information regarding securities temporarily impaired as of March 31, 2014 is summarized below: Less than 12 months 12 months or more Total Fair Value (Estimated) Unrealized Losses Fair Value (Estimated) Unrealized Losses Fair Value (Estimated) Unrealized LossesU.S. Government-sponsored agencies$82,374,000 $(9,131,000) $— $— $82,374,000 $(9,131,000)Mortgage-backed securities81,618,000 (2,758,000) 14,324,000 (742,000) 95,942,000 (3,500,000)State and political subdivisions50,480,000 (2,669,000) 18,918,000 (2,210,000) 69,398,000 (4,879,000)Other equity securities67,000 (2,000) 51,000 (1,000) 118,000 (3,000) $214,539,000 $(14,560,000) $33,293,000 $(2,953,000) $247,832,000 $(17,513,000)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |

| X                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular presentation of available for sale securities, held-to-maturity securities and restricted equity securities as of the balance sheet date.
+ References
No definition available.
+ Details**Name:**fnlc_ScheduleOfAvailableForSaleHeldToMaturityAndNonMarketableSecuritiesTableTextBlock**Namespace Prefix:**fnlc_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments.
+ References
No definition available.
+ Details**Name:**us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of the proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563
+ Details**Name:**us-gaap_ScheduleOfRealizedGainLossTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of investments in an unrealized loss position for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), including: (a) the aggregate related fair value of investments with unrealized losses, (b) the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563
+ Details**Name:**us-gaap_ScheduleOfTemporaryImpairmentLossesInvestmentsTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |