Loans - Pre-Modification and Post-Modification Outstanding Recorded Investment (Details) $ in Thousands	12 Months Ended
Dec. 31, 2022 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	1
Pre-Modification Outstanding Recorded Investment	$ 38
Post-Modification Outstanding Recorded Investment	38
Specific Reserves	$ 0
Commercial \| Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Commercial \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Commercial \| Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Municipal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Residential \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Residential \| Term
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	1
Pre-Modification Outstanding Recorded Investment	$ 38
Post-Modification Outstanding Recorded Investment	38
Specific Reserves	$ 0
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	0
Pre-Modification Outstanding Recorded Investment	$ 0
Post-Modification Outstanding Recorded Investment	0
Specific Reserves	$ 0
Consumer
Accounts, Notes, Loans and Financing Receivable [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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Data Type:	xbrli:integerItemType
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 current period.

+ References

No definition available.

+ Details

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Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- 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

Amortized cost of financing receivable modified during period for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-42

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481933/310-10-55-12A

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-33

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-33

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	duration

- 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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- Details

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- Details

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