Benefit Plans - Summary of Changes in Estimated Fair Value of Level 3 Assets (Details) - Astoria Bank - Pension Benefits - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Significant unobservable inputs:
Fair value at beginning of year	$ 10,288	$ 11,858
Total net gain (loss), realized and unrealized, included in change in net assets	309	(1)
Purchases	9,345	9,000
Sales	(10,796)	(10,569)
Fair value at end of year	9,146	10,288
Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset Unrealized Gain (Loss)	$ 207	$ 210