Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 49,115	$ 48,576
Other comprehensive income before income taxes
Net change in unrealized gain (loss)	4,514	(12,438)
Reclassification adjustment for net losses realized and included in earnings	53	1,929
Amortization of unrealized net gain (loss) on securities transferred to held-to-maturity	665	(2,984)
Other comprehensive income (loss) before income taxes	5,232	(13,493)
Income tax expense (benefit)	1,842	(4,940)
Other comprehensive income (loss) net of income taxes	3,390	(8,553)
Comprehensive income	$ 52,505	$ 40,023