CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Agency MBS, at fair value, pledged as collateral (in dollars)	$ 6,739,499	$ 6,747,299
Non-Agency MBS, at fair value, pledged as collateral (in dollars)	1,851,879	1,602,953
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	895,000	895,000
Common stock, shares issued	358,419	357,546
Common stock, shares outstanding	358,419	357,546
Recourse to the general credit of the Company available to third-party beneficial interest holders in consolidated VIEs	0	0
Preferred Stock | Series A 8.50% Cumulative Redeemable - Liquidation Preference $25.00 per Share
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000	5,000
Preferred stock, dividend rate (as a percent)	8.50%	8.50%
Preferred stock, shares issued	3,840	3,840
Preferred stock, shares outstanding	3,840	3,840
Preferred stock, aggregate liquidation preference (in dollars)	$ 96,000	$ 96,000