Condensed Parent Company Only Financial Statements - Astoria Financial Corporation - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 71,529	$ 88,075	$ 95,916
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred costs	8,806	8,921	9,021
Net cash provided by operating activities	105,019	107,209	134,076
Cash flows from investing activities:
Purchases of securities held-to-maturity	(1,347,939)	(685,918)	(630,366)
Proceeds from maturities of securities held-to-maturity	897,280	515,441	338,691
Net cash provided by investing activities	412,562	596,433	197,948
Cash flows from financing activities:
Common stock repurchases	0	(6,869)	0
Payments relating to treasury shares received for restricted stock award tax payments	(1,913)	0	0
Cash dividends paid to stockholders	(24,989)	(24,856)	(24,643)
Net tax benefit excess from stock-based compensation	0	2,115	192
Net cash used in financing activities	(588,175)	(646,289)	(310,789)
Net (decrease) increase in cash and cash equivalents	(70,594)	57,353	21,235
Cash and cash equivalents at beginning of year	200,538	143,185	121,950
Cash and cash equivalents at end of year	129,944	200,538	143,185
Supplemental disclosure:
Cash paid during the year for interest	121,544	132,687	150,026
Astoria Financial Corporation
Cash flows from operating activities:
Net income	71,529	88,075	95,916
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries	(65,483)	(36,273)	(67,852)
Amortization of deferred costs	404	531	531
Decrease (increase) in other assets, net of other liabilities and amounts due to subsidiaries	810	(1,752)	(484)
Net cash provided by operating activities	7,260	50,581	28,111
Cash flows from investing activities:
Purchases of securities held-to-maturity	(199,861)	0	0
Proceeds from maturities of securities held-to-maturity	160,000	0	0
Net cash provided by investing activities	(39,861)	0	0
Cash flows from financing activities:
Proceeds from issuance of common stock	159	6,168	8,121
Common stock repurchases	0	(6,869)	0
Payments relating to treasury shares received for restricted stock award tax payments	(1,913)	0	0
Cash dividends paid to stockholders	(24,989)	(24,856)	(24,643)
Net tax benefit excess from stock-based compensation	0	2,115	192
Net cash used in financing activities	(26,743)	(23,442)	(16,330)
Net (decrease) increase in cash and cash equivalents	(59,344)	27,139	11,781
Cash and cash equivalents at beginning of year	102,338	75,199	63,418
Cash and cash equivalents at end of year	42,994	102,338	75,199
Supplemental disclosure:
Cash paid during the year for interest	$ 12,500	$ 12,500	$ 12,500