Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Balance Sheets [Abstract]
Mortgage-backed securities, pledged assets	$ 17,012,472	$ 9,089,295
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	76,823,220	46,115,990
Common stock, shares outstanding	76,823,220	46,115,990