Statements Of Assets And Liabilities (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Feb. 01, 2012	Dec. 31, 2011	Dec. 31, 2010
Statements Of Assets And Liabilities [Abstract]
Investments in securities, pledged assets		$ 8,412,295	$ 3,671,582
Accrued interest payable, accrued interest on repurchase agreements		$ 3,747	$ 1,084
Common stock, par value		$ 0.01	$ 0.01
Common stock, shares authorized		500,000,000	500,000,000
Common stock, shares issued		82,753,000	59,551,000
Common stock, shares outstanding	111,688,636	82,753,000	59,551,000