Stockholders' Equity (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period			$ 754,453
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	$ 0	$ 0	4,537	$ 0
Net OCI during the period	(64,248)	58,848	(59,873)	113,338
Balance at end of period	694,580		694,580
Net Unrealized Gain/(Loss) on AFS Securities
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period	850,257	819,222	813,515	752,912
OCI before reclassifications	(82,945)	93,230	(43,767)	162,491
Amounts reclassified from AOCI	(8,161)	(6,748)	(15,134)	(9,699)
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	0		4,537
Net OCI during the period	(91,106)	86,482	(54,364)	152,792
Balance at end of period	759,151	905,704	759,151	905,704
Net Unrealized Gain/(Loss) on Swaps
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period	(91,429)	(27,037)	(59,062)	(15,217)
OCI before reclassifications	26,858	(27,634)	(5,509)	(39,901)
Amounts reclassified from AOCI	0	0	0	447
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	0		0
Net OCI during the period	26,858	(27,634)	(5,509)	(39,454)
Balance at end of period	(64,571)	(54,671)	(64,571)	(54,671)
Total AOCI
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period	758,828	792,185	754,453	737,695
OCI before reclassifications	(56,087)	65,596	(49,276)	122,590
Amounts reclassified from AOCI	(8,161)	(6,748)	(15,134)	(9,252)
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	0		4,537
Net OCI during the period	(64,248)	58,848	(59,873)	113,338
Balance at end of period	$ 694,580	$ 851,033	$ 694,580	$ 851,033