CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 19,490	$ 18,008	$ 42,908	$ 64,630
Available-for-sale Agency MBS, fair value adjustment	(13,625)	10,247	62,104	(198,882)
Reclassification adjustment for loss (gain) on sales of Agency MBS included in net income	5,617	(1,991)	4,022	(9,237)
Unrealized gains (losses) on derivatives	987	(40,863)	(73,959)	(10,715)
Reclassification adjustment for interest expense on swap agreements included in net income	13,382	14,633	53,372	38,426
Other comprehensive income (loss)	6,361	(17,974)	45,539	(180,408)
Comprehensive income (loss)	$ 25,851	$ 34	$ 88,447	$ (115,778)