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Details of Interest Income on Non accrual loans (Detail) - Non-Covered Loans - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Interest income that would have been recorded | $ 4,974 | $ 3,128 | $ 2,288
Interest income actually recorded | (2,904) | (1,708) | (1,574)
Interest income foregone | $ 2,070 | $ 1,420 | $ 714

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- Definition Reflects the amount of interest income on impaired and nonperforming loans that would have been recorded during the reporting period. + References No definition available. + Details
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Namespace Prefix: | nyb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Financing Receivable, Impaired, Interest Lost on Non Accrual Loans + References No definition available. + Details
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Namespace Prefix: | nyb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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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
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Definition Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524 + Details
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Balance Type: | credit
Period Type: | duration

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- Details
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