Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
ASSETS
Pledged MBS	$ 4,127,459	$ 3,967,134
Shareholders' Equity:
Preferred Stock, Par Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	8,000,000	8,000,000
Preferred Stock, Shares Issued	2,300,000	2,300,000
Preferred Stock, Shares Outstanding	2,300,000	2,300,000
Preferred Stock, aggregate liquidation preference	$ 58,532	$ 58,532
Common stock, par value	$ 0.01	$ 0.01
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	54,835,420	54,268,915
Common stock, shares outstanding	54,835,420	54,268,915