Loan Modification Program, Extension For Payment Deferral Period

No definition available.

Name:	nfbk_LoanModificationProgramExtensionForPaymentDeferralPeriod
Namespace Prefix:	nfbk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Loan Modification Program, Payment Deferral Period

+ References

No definition available.

+ Details

Name:	nfbk_LoanModificationProgramPaymentDeferralPeriod
Namespace Prefix:	nfbk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Trouble Debt Restructuring Amount.

+ References

No definition available.

+ Details

Name:	nfbk_TroubleDebtRestructuringAmount
Namespace Prefix:	nfbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationNameAxis=nfbk_COVID19Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Narrative, Troubled Debt Restructurings (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) contract	Jun. 30, 2021 contract	Jun. 30, 2022 USD ($) contract	Jun. 30, 2021 contract	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings \| $	$ 7.3		$ 7.3		$ 9.0
Number of TDR loans restructured that subsequently defaulted (contract)			0	0
COVID-19
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of contracts	0	0	0	0
Loan modification program, payment deferral period			90 days
Loan modification program, extension for payment deferral period			90 days