Stockholders' Equity - AOCI (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, ending balance	$ 754,453	$ 737,695
Reclassification out of Accumulated Other Comprehensive Income
Components of Accumulated Other Comprehensive Income (Loss)
Amounts reclassified from AOCI	(34,501)	(19,833)	(8,693)
Net Unrealized Gain/(Loss) on Available-for-Sale MBS and CRT securities
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance	752,912	824,808	55,491
OCI before reclassifications	95,551	(52,063)	778,010
Amounts reclassified from AOCI	(34,948)	(19,833)	(8,693)
Net OCI during the period	60,603	(71,896)	769,317
AOCI, ending balance	813,515	752,912	824,808
Net Unrealized Gain/(Loss) on Swaps
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance	(15,217)	(62,831)	(114,194)
OCI before reclassifications	(44,292)	47,614	51,363
Amounts reclassified from AOCI	447	0	0
Net OCI during the period	(43,845)	47,614	51,363
AOCI, ending balance	(59,062)	(15,217)	(62,831)
Accumulated Other Comprehensive Income/(Loss):
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance	737,695	761,977	(58,703)
OCI before reclassifications	51,259	(4,449)	829,373
Amounts reclassified from AOCI	(34,501)	(19,833)	(8,693)
Net OCI during the period	16,758	(24,282)	820,680
AOCI, ending balance	$ 754,453	$ 737,695	$ 761,977