Consolidated Balance Sheets (Parenthetical) (USD $) Share data in Thousands, except Per Share data	Jun. 30, 2011	Dec. 31, 2010
Mortgage securities and similar investments, pledged under repurchase arrangements	$ 10,960,000,000	$ 8,220,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000	250,000
Common stock, shares issued	81,311	70,259
Common stock, shares outstanding	81,311	70,259
$1.60 Cumulative Preferred Stock, Series A
Preferred stock, shares issued	187	187
Preferred stock, shares outstanding	187	187
Preferred stock, aggregate liquidation preference	3,072,000	3,072,000
Preferred Stock [Member]
Preferred stock, par value	$ 0.1	$ 0.1
Preferred stock, shares authorized	100,000	100,000
$1.26 Cumulative Convertible Preferred Stock, Series B
Preferred stock, shares issued	15,865	15,819
Preferred stock, shares outstanding	15,865	15,819
Preferred stock, aggregate liquidation preference	$ 180,543,000	$ 180,543,000