Stockholders' Equity (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Components of accumulated other comprehensive income/(loss)
Accumulated other comprehensive income/(loss)	$ 761,977
Other Comprehensive Income	130,395	269,554
Accumulated other comprehensive income/(loss)	892,372
Net Unrealized Gain on Available-for-Sale MBS
Components of accumulated other comprehensive income/(loss)
Accumulated other comprehensive income/(loss)	824,808
OCI before reclassifications	119,439
Amounts reclassified from AOCI	(1,360)
Other Comprehensive Income	118,079
Accumulated other comprehensive income/(loss)	942,887
Net Unrealized (Loss)/Gain on Swaps
Components of accumulated other comprehensive income/(loss)
Accumulated other comprehensive income/(loss)	(62,831)
OCI before reclassifications	12,316
Other Comprehensive Income	12,316
Accumulated other comprehensive income/(loss)	(50,515)
Total AOCI
Components of accumulated other comprehensive income/(loss)
Accumulated other comprehensive income/(loss)	761,977
OCI before reclassifications	131,755
Amounts reclassified from AOCI	(1,360)
Other Comprehensive Income	130,395
Accumulated other comprehensive income/(loss)	$ 892,372