Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Mortgage-backed securities, pledged assets	$ 14,904,322	$ 16,538,214
Mortgage loans held for investment, pledged assets	27,835	0
Pledged cash	493,021	323,791
Mortgage loans held for sale, pledged assets	$ 9,572	$ 0
Series A preferred stock dividend rate per year	7.625%	7.625%
7.625% Series A Cumulative Redeemable Preferred stock, par value	$ 0.001	$ 0.001
7.625% Series A Cumulative Redeemable Preferred stock, shares authorized	25,000,000	25,000,000
7.625% Series A Cumulative Redeemable Preferred stock, shares issued	11,500,000	11,500,000
7.625% Series A Cumulative Redeemable Preferred stock, shares outstanding	11,500,000	11,500,000
7.625% Series A Cumulative Redeemable Preferred stock, aggregate Liquidation Preference	$ 287,500	$ 287,500
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	96,770,690	96,770,690
Common stock, shares outstanding	96,771,158	96,771,158