CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Agency MBS, at fair value, pledged as collateral (in dollars)	$ 6,404,803	$ 6,142,306
Non-Agency MBS, at fair value, pledged as collateral (in dollars)	1,776,353	1,778,067
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	8,050	8,050
Preferred stock, dividend rate (as a percent)	7.50%	7.50%
Preferred stock, shares issued	8,000	8,000
Preferred stock, shares outstanding	8,000	8,000
Preferred stock, aggregate liquidation preference (in dollars)	$ 200,000	$ 200,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	886,950	886,950
Common stock, shares issued	366,217	365,125
Common stock, shares outstanding	366,217	365,125