Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Pledged securities	$ 645,267,000	$ 639,683,000
Assets of consolidated VIE	7,432,157,000	7,413,082,000
Liabilities of consolidated VIE	$ 7,175,369,000	$ 7,077,175,000
Preferred stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	200,000,000	200,000,000
Preferred stock, shares issued (in shares)	6,600,000	6,600,000
Preferred stock, shares outstanding (in shares)	6,600,000	6,600,000
Common stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	109,409,236	109,401,721
Common stock, shares outstanding (in shares)	109,409,236	109,401,721
Series B Preferred Stock
Preferred stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Preferred stock, cumulative redeemable dividend rate	7.75%	7.75%
Preferred stock, liquidation preference per share (in Dollars per share)	$ 25	$ 25
Preferred stock, shares authorized (in shares)	6,000,000	6,000,000
Preferred stock, shares issued (in shares)	3,000,000	3,000,000
Preferred stock, shares outstanding (in shares)	3,000,000	3,000,000
Series C Preferred Stock
Preferred stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Preferred stock, cumulative redeemable dividend rate	7.875%	7.875%
Preferred stock, liquidation preference per share (in Dollars per share)	$ 25	$ 25
Preferred stock, shares authorized (in shares)	4,140,000	4,140,000
Preferred stock, shares issued (in shares)	3,600,000	3,600,000
Preferred stock, shares outstanding (in shares)	3,600,000	3,600,000
Available-for-sale securities
Assets held in securitization trusts	$ 41,490,000	$ 40,734,000
Distressed residential mortgage loans held in securitization trust, (net)
Loans, carrying value	$ 0	$ 114,214,000