Summary of Portfolio of Securities Held to Maturity (Parenthetical) (Detail) (Held-to-maturity Securities, USD $)	Sep. 30, 2013	Dec. 31, 2012
Held-to-maturity Securities
Schedule of Held-to-maturity Securities [Line Items]
Non-credit portion of OTTI recorded in AOCL, before taxes	$ 9,200,000	$ 21,600,000

Accumulated Other Comprehensive Income Loss Noncredit Portion of Other Than Temporarily Impaired Securities Before Tax

No definition available.

Name:	nyb_AccumulatedOtherComprehensiveIncomeLossNoncreditPortionOfOtherThanTemporarilyImpairedSecuritiesBeforeTax
Namespace Prefix:	nyb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant