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Investment Securities Additional Information (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
state
security
Mar. 31, 2014
security
Dec. 31, 2014
security
Sep. 30, 2014
Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]          
Available-for-sale Securities Pledged as Collateral $ 224,133us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral $ 132,657us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral $ 164,919us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral    
Number of securities temporarily impaired 55fnlc_NumberOfSecuritiesTemporarilyImpaired 268fnlc_NumberOfSecuritiesTemporarilyImpaired 56fnlc_NumberOfSecuritiesTemporarilyImpaired    
Number of securities temporarily impaired 5fnlc_NumberOfSecuritiesTemporarilyImpairedTwelveMonths 73fnlc_NumberOfSecuritiesTemporarilyImpairedTwelveMonths 36fnlc_NumberOfSecuritiesTemporarilyImpairedTwelveMonths    
Length of time securities temporarily impaired 12 months 12 months 12 months    
Amortized cost of transferred securities from available-for-sale to held-to-maturity       89,780fnlc_AvailableforSaleSecuritiesTransferredSecurityatCarryingValue  
Fair value of transferred securities from available-for-sale to held-to-maturity       89,757fnlc_AvailableforSaleSecuritiesTransferredSecurityatFairValue  
Net unrealized loss, net of taxes on transferred securities       15fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesAccumulatedUnrealizedGainLoss  
Other comprehensive income (loss), unrealized loss on transferred securities 67fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity 0fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity 48fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity   0fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity
Number of states in New England where FHLB serve 6fnlc_NumberOfStatesInNewEnglandWhereFhlbServe        
Federal Home Loan Bank Stock $ 12,875us-gaap_FederalHomeLoanBankStock $ 12,875us-gaap_FederalHomeLoanBankStock $ 12,875us-gaap_FederalHomeLoanBankStock