Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Residential mortgage investments, pledged under repurchase arrangements	$ 12,696,827	$ 11,929,514
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000	250,000
Common stock, shares issued	92,951	92,951
Common stock, shares outstanding	88,287	88,287
$1.60 Cumulative Preferred Stock, Series A [Member]
Preferred stock, dividend rate	$ 1.60	$ 1.60
Preferred stock, shares issued	186	186
Preferred stock, shares outstanding	186	186
Preferred stock, aggregate liquidation preference	3,054	3,056
$1.26 Cumulative Convertible Preferred Stock, Series B [Member]
Preferred stock, dividend rate	$ 1.26	$ 1.26
Preferred stock, shares issued	16,415	16,415
Preferred stock, shares outstanding	16,184	16,184
Preferred stock, aggregate liquidation preference	$ 186,800	$ 184,175
Preferred Stock [Member]
Preferred stock, par value	$ 0.1	$ 0.1
Preferred stock, shares authorized	100,000	100,000