Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Mortgage-backed securities, pledged assets	$ 11,540,366	$ 13,932,415
Mortgage loans held for investment, pledged assets	47,176	50,143
Pledged cash	469,690	376,081
Mortgage loans held for sale, pledged assets	$ 25,919	$ 17,542
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	94,529,206	95,773,767
Common stock, shares outstanding	94,529,206	95,773,767
Asset of collateralized financing entity	$ 216,224	$ 228,240
Liabilities of collateralized financing entity	$ 60,712	$ 57,784