Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 85,628	$ 82,607	$ 75,610
Change in net unrealized (loss) gain on available-for-sale (AFS) securities, net of tax	6,452	5,120	5,820
Accretion of the net unrealized loss on the transfer of AFS securities to held-to-maturity (HTM) securities, net of tax	5	4	5
Change in defined benefit pension plan, net of tax	16,244	(4,114)	(11,927)
Comprehensive income, net of tax	$ 108,329	$ 83,617	$ 69,508