Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Mortgage-backed securities, pledged assets	$ 24,857,784	$ 17,012,472
7.625% Series A Cumulative Redeemable Preferred stock, par value	$ 0.001	$ 0.001
7.625% Series A Cumulative Redeemable Preferred stock, shares authorized	25,000,000	25,000,000
7.625% Series A Cumulative Redeemable Preferred stock, shares issued	11,500,000	0
7.625% Series A Cumulative Redeemable Preferred stock, shares outstanding	11,500,000	0
7.625% Series A Cumulative Redeemable Preferred stock, Aggregate Liquidation Preference	$ 287,500	$ 287,500
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	98,809,404	76,823,220
Common stock,shares outstanding	98,809,404	76,823,220