Regulatory Capital Requirements under Banking Regulations [Abstract]

No definition available.

Name:	nfbk_RegulatoryCapitalRequirementsUnderBankingRegulationsAbstract
Namespace Prefix:	nfbk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Tier One Common Capital Required for Capital Adequacy to Risk Weighted Assets

+ References

No definition available.

+ Details

Name:	nfbk_TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets
Namespace Prefix:	nfbk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier One Common Capital Required to be Well Capitalized to Risk Weighted Assets

+ References

No definition available.

+ Details

Name:	nfbk_TierOneCommonCapitalRequiredtobeWellCapitalizedtoRiskWeightedAssets
Namespace Prefix:	nfbk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier One Common Capital to Risk Weighted Assets, Capital Conservation Buffer

+ References

No definition available.

+ Details

Name:	nfbk_TierOneCommonCapitaltoRiskWeightedAssetsCapitalConservationBuffer
Namespace Prefix:	nfbk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets, Higher Risk Weight

+ References

No definition available.

+ Details

Name:	nfbk_TierOneRiskBasedCapitalRequiredforCapitalAdequacytoRiskWeightedAssetsHigherRiskWeight
Namespace Prefix:	nfbk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio of minimum total risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958570-112826

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio of minimum total risk-based capital to risk-weighted assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio of minimum Tier 1 leverage capital to average assets required for capital adequacy as defined by regulatory framework.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio of minimum Tier 1 leverage capital to average assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio of minimum Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio of minimum Tier 1 risk-based capital to risk-weighted assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Regulatory Requirements - Narrative (Details)	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2019	Jan. 01, 2016
Regulatory Requirements [Abstract]
Common equity Tier 1 capital (to risk-weighted assets), for capital adequacy purposes ratio	4.50%	8.00%
Tier 1 capital (to risk-weighted assets), for capital adequacy purposes ratio	0.06
Total capital (to risk-weighted assets), for capital adequacy purposes ratio	0.080
Tier 1 capital (core) (to adjusted total assets), for capital adequacy purposes ratio	0.040
Tier 1 capital (core) (to adjusted total assets), for well capitalized under prompt corrective action provisions ratio	0.050
Common equity Tier 1 capital (to risk-weighted assets), for well capitalized under prompt corrective action provisions ratio	6.50%	8.00%
Tier 1 risk-based capital ratio	0.080
Total capital (to risk-weighted assets), for well capitalized under prompt corrective action provisions ratio	0.100
Tier 1 risk-based capital required for capital adequacy to risk-weighted assets, higher risk weight	2.50%		2.50%
Capital conservation buffer				0.625%