Certain Information Regarding Health and Welfare Plan (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
Post-Retirement Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	17,280	$ 18,375
Service cost	5	4	$ 4
Interest cost	639	700	759
Actuarial (gain) loss	(673)	(880)
Premiums and claims paid	(957)	(919)
Benefit obligation at end of year	16,294	17,280	18,375
Change in Plan Assets:
Fair value of assets at beginning of year	0	0
Employer contribution	957	919
Premiums and claims paid	(957)	(919)
Fair value of assets at end of year	0	0	$ 0
Funded status (included in "Other liabilities")	(16,294)	(17,280)
Changes recognized in other comprehensive (loss) income for the year ended December 31:
Amortization of prior service cost	249	249
Amortization of actuarial gain	(326)	(383)
Net actuarial (gain) loss arising during the year	(673)	(880)
Total recognized in other comprehensive loss for the year (pre-tax)	(750)	(1,014)
Accumulated other comprehensive loss (pre-tax) not yet recognized in net periodic benefit cost at December 31:
Prior service cost	(1,283)	(1,533)
Actuarial loss, net	5,137	6,137
Total accumulated other comprehensive loss (pre-tax)	$ 3,854	$ 4,604

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

No definition available.

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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.