Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, 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 (loss)	$ 77,891	$ (262,146)	$ 82,212	$ (124,168)
Other comprehensive income:
Net unrealized gains (losses) on securities available for sale	(31,382)	191,227	83,790	(455,185)
Net unrealized gains on derivative instruments	17,923	45,227	75,026	107,952
Other comprehensive income (loss)	(13,459)	236,454	158,816	(347,233)
Comprehensive income (loss)	64,432	(25,692)	241,028	(471,401)
Dividends on preferred stock	5,480	5,481	16,441	16,441
Comprehensive income (loss) available to common shareholders	$ 58,952	$ (31,173)	$ 224,587	$ (487,842)
Comprehensive income (loss) per share - common stock, basic and diluted	$ 0.61	$ (0.32)	$ 2.33	$ (4.94)