Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Mortgage-backed securities, pledged assets	$ 15,660,522	$ 17,049,670
7.625% Series A Cumulative Redeemable Preferred stock, par value	$ 0.001	$ 0.001
7.625% Series A Cumulative Redeemable Preferred stock, shares authorized	25,000,000	25,000,000
7.625% Series A Cumulative Redeemable Preferred stock, shares issued	11,500,000	11,500,000
7.625% Series A Cumulative Redeemable Preferred stock, shares outstanding	11,500,000	11,500,000
7.625% Series A Cumulative Redeemable Preferred stock, aggregate Liquidation Preference	$ 287,500	$ 287,500
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	96,719,908	96,719,908
Common stock, shares outstanding	96,601,523	96,601,523