CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
CONSOLIDATED BALANCE SHEETS
Agency MBS, at fair value, pledged as collateral (in dollars)	$ 6,902,954	$ 6,666,963
Non-Agency MBS, at fair value, pledged as collateral (in dollars)	1,489,463	692,534
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
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	895,000	895,000
Common stock, shares issued	357,013	356,112
Common stock, shares outstanding	357,013	356,112