Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 48,576	$ 18,495
Other comprehensive income:
Net change in unrealized gain	(12,438)	8,018
Reclassification adjustment for net losses realized and included in earnings	1,929	1,829
Amortization of unrealized net gain on securities transferred to held-to-maturity	(2,984)
Other comprehensive income, before income taxes	(13,493)	9,847
Income tax (benefit) expense	(4,940)	3,522
Other comprehensive income	(8,553)	6,325
Comprehensive income	$ 40,023	$ 24,820