CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Agency MBS, at fair value, pledged as collateral (in dollars)	$ 6,282,729	$ 6,747,299
Non-Agency MBS, at fair value, pledged as collateral (in dollars)	1,837,996	1,602,953
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	886,950,000	895,000,000
Common stock, shares issued	365,833,000	357,546,000
Common stock, shares outstanding	365,833,000	357,546,000
Series A 8.50% Cumulative Redeemable - Liquidation Preference
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, dividend rate (as a percent)	8.50%	8.50%
Preferred stock, shares issued	0	3,840,000
Preferred stock, shares outstanding	0	3,840,000
Preferred stock, aggregate liquidation preference (in dollars)	0	96,000
Series B 7.50% Cumulative Redeemable - Liquidation Preference
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0
Preferred stock, shares authorized	8,050,000	0
Preferred stock, dividend rate (as a percent)	7.50%	0.00%
Preferred stock, shares issued	8,000,000	0
Preferred stock, shares outstanding	8,000,000	0
Preferred stock, aggregate liquidation preference (in dollars)	$ 200,000	$ 0