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: |