Other Real Estate Owned (Details) - USD ($)	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Summary Other Real Estate Owned [Abstract]
Real estate acquired in settlement of loans	$ 0	$ 0
Real Estate Owned Valuation Allowance [Roll Forward]
Balance at beginning of year	0	0	$ 45,000
Losses charged to allowance	0	0	(45,000)
Provision charged to operating expenses	0	0	0
Balance at end of year	$ 0	$ 0	$ 0

-- None. No documentation exists for this element. --

No definition available.

Name:	fnlc_SummaryOtherRealEstateOwnedAbstract
Namespace Prefix:	fnlc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11

+ Details

Name:	us-gaap_RealEstateAcquiredThroughForeclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For each period for which an income statement is required, disclosure of the changes in the allowance, including balances at end of period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

Name:	us-gaap_RealEstateOwnedValuationAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the valuation allowance for real estate owned that was applied in the period against the carrying amount of real estate owned that was sold, written down or written off.

+ References

+ Details

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

- Definition

Amount of expense recognized in the income statement for a decrease in valuation of real estate owned (REO).

+ References

+ Details

Name:	us-gaap_RealEstateOwnedValuationAllowanceProvision1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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