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Benefit Plans (Details 11) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Benefit Plans    
Net actuarial loss that will be recognized as components of net periodic cost in 2014 $ 3,000,000af_DefinedBenefitPlanExpectedFutureNetActuarialLoss  
Prior service cost that will be recognized as components of net periodic cost in 2014 190,000af_DefinedBenefitPlanExpectedFuturePriorServiceCost  
Accumulated benefit obligation 270,300,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation 230,400,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Pension benefits    
Benefit Plans    
Employer contribution 5,615,000us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
5,648,000us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Astoria Bank | Pension benefits    
Benefit Plans    
Employer contribution $ 5,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= af_AstoriaBankMember
 
Astoria Bank | Pension benefits | Astoria Financial Corporation common stock | Maximum    
Benefit Plans    
Equity securities percentage in total plan assets 10.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ invest_InvestmentIssuerAxis
= af_AstoriaFinancialCorporationCommonStockMember
/ dei_LegalEntityAxis
= af_AstoriaBankMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember