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Activity in Allowance for Losses on Covered Loans (Detail) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2017 | Mar. 31, 2016
Valuation Allowance [Line Items] |  |
Balance, beginning of period | $ 23,701 | $ 31,395
Provision for (recovery of) losses | (4,008) | (176)
Balance, end of period | 17,906 | 28,498
Covered |  |
Valuation Allowance [Line Items] |  |
Provision for (recovery of) losses | $ (5,795) | $ (2,897)

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- Definition Provision Recoveries For Loan Losses + References No definition available. + Details
Name: | nyb_ProvisionRecoveriesForLoanLosses
Namespace Prefix: | nyb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of allowance for loan and lease losses covered by loss sharing agreements. + References No definition available. + Details
Name: | us-gaap_LoansAndLeasesReceivableAllowanceCovered
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Details
Name: | us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAxis=nyb_CoveredMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |