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Effect of Derivative Instruments on Consolidated Statements of Income and Comprehensive Income (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Included in Mortgage Banking Income $ 5,571us-gaap_DerivativeGainLossOnDerivativeNet $ 3,041us-gaap_DerivativeGainLossOnDerivativeNet
Treasury Options    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Included in Mortgage Banking Income 3,416us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= nyb_TreasuryOptionsMember		 (399)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= nyb_TreasuryOptionsMember
Eurodollar Futures    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Included in Mortgage Banking Income 383us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		 (55)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember
Forward commitments to buy/sell loans/mortgage-backed securities    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (Loss) Included in Mortgage Banking Income $ 1,772us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= nyb_ForwardCommitmentsToBuyAndSellLoansAndSecuritiesMember		 $ 3,495us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= nyb_ForwardCommitmentsToBuyAndSellLoansAndSecuritiesMember