Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income	$ 62,121	$ 56,808	$ 51,008
Other Comprehensive Income (Loss), Net of Tax:
Change in net unrealized gains (losses) on investment securities available-for-sale, net of tax expense (benefit) of $1,222, $(3,325), and $505 for the years ended December 31, 2014, 2013, and 2012, respectively	2,270	(6,177)	938
Reclassification adjustment for realized gain on sale of investment securities available-for-sale included in net income, net of tax expense of $311 for the year ended December 31, 2013	0	(577)	0
Change in adjustment for pension and other postretirement benefits, net of tax benefit (expense) of $7,648, $(9,344), and $3,623 for the years ended December 31, 2014, 2013, and 2012, respectively	(14,203)	17,353	(6,728)
Total other comprehensive income (loss), net of tax	(11,933)	10,599	(5,790)
Comprehensive Income	$ 50,188	$ 67,407	$ 45,218