Loans - Pre-Modification and Post-Modification Outstanding Recorded Investment (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) loan	Mar. 31, 2017 loan
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	7	0
Pre-Modification Outstanding Recorded Investment	$ 1,056
Post-Modification Outstanding Recorded Investment	1,056
Specific Reserves	$ 36
Commercial \| Real estate
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	7
Pre-Modification Outstanding Recorded Investment	$ 1,056
Post-Modification Outstanding Recorded Investment	1,056
Specific Reserves	$ 36
Commercial \| Construction
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Commercial \| Other
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Municipal
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Residential \| Construction
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Residential \| Term
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Home equity line of credit
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Consumer
Financing Receivable, Modifications [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0

The number of financing receivables that have been modified by troubled debt restructurings during the current period.

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

Specific allowance for loan and lease losses on receivable financings that are classified as troubled debt restructurings during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

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Period Type:	duration

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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