XML 66 R27.htm IDEA: XBRL DOCUMENT v3.2.0.727

Securities Available-for-Sale (Gross Unrealized Losses on Mortgage-Backed Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	$ 104	$ 33
Estimated Fair value, less than 12 months	43,622	13,356
Unrealized losses, 12 months or more	9,726	10,326
Estimated Fair value, 12 months or more	245,091	292,448
Unrealized losses, total	9,830	10,359
Estimated fair value, total	288,713	305,804
Pass-through Certificates | GSE
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	84	1
Estimated Fair value, less than 12 months	15,157	181
Unrealized losses, 12 months or more	1,333	1,130
Estimated Fair value, 12 months or more	56,575	61,526
Unrealized losses, total	1,417	1,131
Estimated fair value, total	71,732	61,707
Real estate mortgage investment conduits (REMICs) | GSE
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	18	30
Estimated Fair value, less than 12 months	16,860	3,179
Unrealized losses, 12 months or more	8,360	9,162
Estimated Fair value, 12 months or more	187,705	229,896
Unrealized losses, total	8,378	9,192
Estimated fair value, total	204,565	233,075
Real estate mortgage investment conduits (REMICs) | Non-GSE
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	0	0
Estimated Fair value, less than 12 months	0	0
Unrealized losses, 12 months or more	33	34
Estimated Fair value, 12 months or more	811	1,026
Unrealized losses, total	33	34
Estimated fair value, total	811	1,026
Other securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	2	2
Estimated Fair value, less than 12 months	11,605	9,996
Unrealized losses, 12 months or more		0
Estimated Fair value, 12 months or more		0
Unrealized losses, total	2	2
Estimated fair value, total	$ 11,605	$ 9,996

X

- Definition

Available-for-sale Securities, Continuous Unrealized Loss Position,12 Months or Longer, Aggregate Losses Accumulated in AOCI

+ References

No definition available.

+ Details

Name:	nfbk_AvailableforsaleSecuritiesContinuousUnrealizedLossPosition12MonthsorLongerAggregateLossesAccumulatedinAOCI
Namespace Prefix:	nfbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated in AOCI

+ References

No definition available.

+ Details

Name:	nfbk_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionAggregateLossesAccumulatedinAOCI
Namespace Prefix:	nfbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated in AOCI

+ References

No definition available.

+ Details

Name:	nfbk_AvailableforsaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLossesAccumulatedinAOCI
Namespace Prefix:	nfbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 320



-SubTopic 10



-Section 50



-Paragraph 6



-Subparagraph (a)(1)



-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

+ Details

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

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 320



-SubTopic 10



-Section 50



-Paragraph 7



-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563



Reference 2: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 320



-SubTopic 10



-Section 50



-Paragraph 6



-Subparagraph (a)(1)



-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

+ Details

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

X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 320



-SubTopic 10



-Section 50



-Paragraph 6



-Subparagraph (a)(1)



-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563



Reference 2: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 320



-SubTopic 10



-Section 50



-Paragraph 7



-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

+ Details

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

X

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

X

- Details

Name:	us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis=nfbk_PassThroughCertificatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis=nfbk_RealEstateMortgageInvestmentsConduitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=nfbk_NonUsGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis=nfbk_OtherAvailableForSaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: