Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (83,892)	$ 77,891	$ (93,871)	$ 82,212
Other comprehensive income (loss):
Net unrealized gains (losses) on securities available for sale	(1,902)	(31,382)	(608)	83,790
Net unrealized gains on derivative instruments	6,389	17,923	26,139	75,026
Other comprehensive income (loss)	4,487	(13,459)	25,531	158,816
Comprehensive income (loss)	(79,405)	64,432	(68,340)	241,028
Dividends on preferred stock	5,480	5,480	16,441	16,441
Comprehensive income (loss) available to common shareholders	$ (84,885)	$ 58,952	$ (84,781)	$ 224,587