Stockholders' Equity - AOCI (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance		$ 754,453
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing		4,537	$ 0	$ 0
AOCI, ending balance		515,851	754,453
Reclassification out of Accumulated Other Comprehensive Income
Components of Accumulated Other Comprehensive Income (Loss)
Amounts reclassified from AOCI		(37,912)	(34,501)	(19,833)
Net Unrealized Gain/(Loss) on AFS Securities
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance		813,515	752,912	824,808
OCI before reclassifications		(194,890)	95,551	(52,063)
Amounts reclassified from AOCI	[1]	(37,912)	(34,948)	(19,833)
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing		4,537	0	0
Net OCI during the period	[2]	(228,265)	60,603	(71,896)
AOCI, ending balance		585,250	813,515	752,912
Net Unrealized Gain/(Loss) on Swaps
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance		(59,062)	(15,217)	(62,831)
OCI before reclassifications		(10,337)	(44,292)	47,614
Amounts reclassified from AOCI	[1]	0	447	0
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing		0	0	0
Net OCI during the period	[2]	(10,337)	(43,845)	47,614
AOCI, ending balance		(69,399)	(59,062)	(15,217)
Accumulated Other Comprehensive Income
Components of Accumulated Other Comprehensive Income (Loss)
AOCI, beginning balance		754,453	737,695	761,977
OCI before reclassifications		(205,227)	51,259	(4,449)
Amounts reclassified from AOCI	[1]	(37,912)	(34,501)	(19,833)
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing		4,537	0	0
Net OCI during the period	[2]	(238,602)	16,758	(24,282)
AOCI, ending balance		$ 515,851	$ 754,453	$ 737,695

[1] See separate table below for details about these reclassifications.

[2] For further information regarding changes in OCI, see the Company’s consolidated statements of comprehensive income/(loss).