CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Beginning Balance at Dec. 31, 2014	$ 1,390,771	$ 183,936	$ 958	$ 1,325,340	$ (346,885)	$ 227,422
Net income	108,325				108,325
Change in unrealized gain on mortgage securities, net	(98,202)					(98,202)
Amounts related to cash flow hedges, net	6,875					6,875
Cash dividends:
Common	(109,217)			(16,473)	(92,744)
Preferred	(15,160)				(15,160)
Issuance of Series E preferred stock	13,236	13,236
Other additions to capital	1,696			1,696
Ending Balance at Dec. 31, 2015	1,298,324	197,172	958	1,310,563	(346,464)	136,095
Net income	82,873				82,873
Change in unrealized gain on mortgage securities, net	(48,894)					(48,894)
Amounts related to cash flow hedges, net	18,585					18,585
Cash dividends:
Common	(91,093)			(23,592)	(67,501)
Preferred	(15,372)				(15,372)
Issuance of Series E preferred stock	1,887	1,887
Other additions to capital	1,377		2	1,375
Ending Balance at Dec. 31, 2016	1,247,687	199,059	960	1,288,346	(346,464)	105,786
Cumulative effect adjustment- adoption of ASU 2017-12					(105)	105
Net income	79,589				79,589
Change in unrealized gain on mortgage securities, net	(60,391)					(60,391)
Amounts related to cash flow hedges, net	16,618					16,618
Cash dividends:
Common	(76,732)			(14,584)	(62,148)
Preferred	(17,442)				(17,442)
Issuance of Series E preferred stock	51,887	51,887
Common stock repurchases	(3,460)		(4)	(3,456)
Other additions to capital	1,120		1	1,119
Ending Balance at Dec. 31, 2017	$ 1,238,876	$ 250,946	$ 957	$ 1,271,425	$ (346,570)	$ 62,118