Stockholders' Equity (Details 2) (USD $)			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Net Unrealized Gain on Available-for-Sale MBS	Dec. 31, 2012 Net Unrealized (Loss)/Gain on Swaps	Dec. 31, 2012 Accumulated Other Comprehensive Income/(Loss):
Components of accumulated other comprehensive income/(loss)
Accumulated other comprehensive income/(loss)	$ 761,977,000	$ (58,703,000)	$ 55,491,000	$ (114,194,000)	$ (58,703,000)
Current period other comprehensive income			769,317,000	51,363,000	820,680,000
Accumulated other comprehensive income/(loss)	761,977,000	(58,703,000)	824,808,000	(62,831,000)	761,977,000
Accumulated Other Comprehensive Income/(Loss)
Other-than-temporary impairments recognized in accumulated other comprehensive(loss)/income	$ 2,600,000	$ 65,400,000