Stockholders' Equity (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 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	(96,286)	(33,499)	(156,159)	79,839
Balance at end of period	598,294		598,294
Net Unrealized Gain/(Loss) on AFS Securities
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period	759,151	905,704	813,515	752,912
OCI before reclassifications	(44,039)	(43,410)	(87,184)	116,973
Amounts reclassified from AOCI	(11,363)	(13,589)	(27,119)	(21,180)
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	0		4,537
Net OCI during the period	(55,402)	(56,999)	(109,766)	95,793
Balance at end of period	703,749	848,705	703,749	848,705
Net Unrealized Gain/(Loss) on Swaps
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period	(64,571)	(54,671)	(59,062)	(15,217)
OCI before reclassifications	(40,884)	23,500	(46,393)	(16,401)
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	(40,884)	23,500	(46,393)	(15,954)
Balance at end of period	(105,455)	(31,171)	(105,455)	(31,171)
Total AOCI
Components of accumulated other comprehensive income/(loss)
Balance at beginning of period	694,580	851,033	754,453	737,695
OCI before reclassifications	(84,923)	(19,910)	(133,577)	100,572
Amounts reclassified from AOCI	(11,363)	(13,589)	(27,119)	(20,733)
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	0		4,537
Net OCI during the period	(96,286)	(33,499)	(156,159)	79,839
Balance at end of period	$ 598,294	$ 817,534	$ 598,294	$ 817,534