v3.25.3

Note 5 - Mortgage Operations - Schedule of Servicing Assets, At Amortized Value (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2025
Mortgage servicing rights, balance	$ 1,242	$ 1,312
Mortgage servicing rights, additions	10	34
Mortgage servicing rights, reductions	(46)	(140)
Mortgage servicing rights, balance	1,206	1,206
Valuation allowance, balance	0	0
Valuation allowance, additions	0	0
Valuation allowance, reductions	0	0
Valuation allowance, balance	0	0
Mortgage servicing rights, net of valuation allowance, balance	1,242	1,312
Mortgage servicing rights, net of valuation allowance, additions	10	34
Mortgage servicing rights, net of valuation allowance, reductions	(46)	(140)
Mortgage servicing rights, net of valuation allowance, balance	$ 1,206	$ 1,206

Amortized carrying amount (balance) as of the balance sheet date of an asset representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements, net of valuation allowance.

+ References

No definition available.

+ Details

Name:	fnrn_ServicingAssetAtAmortizedCostNetOfValuationAllowance
Namespace Prefix:	fnrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The value of new servicing assets, subsequently measured at amortized value, acquired or created during the current period through purchases or from transfers of financial assets, net of valuation allowance.

+ References

No definition available.

+ Details

Name:	fnrn_ServicingAssetAtAmortizedCostNetOfValuationAllowanceAdditions
Namespace Prefix:	fnrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense charged against earnings for the periodic recognition of servicing assets relative to estimated net servicing income, net of valuation allowance.

+ References

No definition available.

+ Details

Name:	fnrn_ServicingAssetAtAmortizedCostNetOfValuationAllowanceReductions
Namespace Prefix:	fnrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481260/860-50-45-1

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481260/860-50-45-2

+ Details

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

- Definition

Amount of additions from purchases, assumption or transfer to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-4

+ Details

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

- Definition

Amount conveyed to unrelated parties of contract to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-4

+ Details

Name:	us-gaap_ServicingAssetAtAmortizedValueDisposals
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the estimated amount of impairment as of the balance sheet date of recognized servicing assets that are being amortized in proportion to and over the period of estimated net servicing income or loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-4

+ Details

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

- Definition

Amount of increase in the valuation allowance for impairment of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer from charges to expense.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-4

+ Details

Name:	us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of decrease in the valuation allowance for impairment of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer from recoveries recognized.

+ References

+ Details

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

FIRST NORTHERN COMMUNITY BANCORP 10-Q