Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 33,202	$ 46,984	$ 128,640	$ 104,783
Other comprehensive income:
Net change in unrealized gains and losses	(9,685)	10,821	(96,074)	24,410
Reclassification adjustment for net losses realized and included in earnings	1,553	842	5,835	4,371
Amortization of unrealized net gain on securities transferred to held-to-maturity	(1,456)	(2,725)	(7,099)	(5,645)
Other comprehensive income, before income taxes	(9,588)	8,938	(97,338)	23,136
Income tax expense (benefit)	(3,512)	3,263	(35,492)	8,413
Other comprehensive (loss)/income	(6,076)	5,675	(61,846)	14,723
Comprehensive income	$ 27,126	$ 52,659	$ 66,794	$ 119,506