Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 33,260	$ 22,170	$ 96,631	$ 65,968
Change in net unrealized gain (loss) on available-for-sale (AFS) securities, net of tax	1,635	2,977	18,445	1,210
Accretion of the net unrealized loss on the transfer of AFS securities to held-to-maturity (HTM) securities, net of tax	2	2	4	4
Change in pension plan assets, net of tax	309	740	928	2,223
Comprehensive income, net of tax	$ 35,206	$ 25,889	$ 116,008	$ 69,405