Retirement Plan, Based on Measurement Date (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in Plan Assets:
Fair value of assets at end of year	$ 220,740
Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	146,618	$ 157,061
Interest cost	5,881	6,063	$ 5,895
Actuarial loss (gain)	611	(7,891)
Annuity payments	(6,473)	(6,339)
Settlements	(208)	(2,276)
Benefit obligation at end of year	146,429	146,618	157,061
Change in Plan Assets:
Fair value of assets at beginning of year	211,888	222,990
Actual return (loss) on plan assets	15,533	(2,487)
Contributions	0	0
Annuity payments	(6,473)	(6,339)
Settlements	(208)	(2,276)
Fair value of assets at end of year	220,740	211,888	$ 222,990
Funded status (included in "Other assets")	74,311	65,270
Changes recognized in other comprehensive income (loss) for the year ended December 31:
Amortization of prior service cost	0	0
Amortization of actuarial loss	(9,050)	(8,208)
Net actuarial loss arising during the year	706	12,155
Total recognized in other comprehensive loss for the year (pre-tax)	(8,344)	3,947
Accumulated other comprehensive loss (pre-tax) not yet recognized in net periodic benefit cost at December 31:
Prior service cost	0	0
Actuarial loss, net	79,541	87,885
Total accumulated other comprehensive loss (pre-tax)	$ 79,541	$ 87,885

Other Comprehensive Income, Amortization of Net Actuarial Gain (Loss), Before Tax

No definition available.

Name:	nyb_OtherComprehensiveIncomeAmortizationOfNetActuarialGainLossBeforeTax
Namespace Prefix:	nyb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.