Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 108,032	$ 86,830	$ 62,121
Other Comprehensive Income (Loss), Net of Tax:
Unrealized holding gains (losses) on securities available-for-sale arising during the period	(18,723)	(1,952)	3,492
Reclassification adjustment for gains on realized income	(129)	(630)	0
Tax effect	6,598	904	(1,222)
Net unrealized gains (losses) on securities available-for-sale, net of tax	(12,254)	(1,678)	2,270
Pension plan remeasurement	(707)	0	0
Adjustment for pension and other postretirement benefits	2,630	7,845	(21,851)
Tax effect	(673)	(2,746)	7,648
Net adjustment for pension and other postretirement benefits	1,250	5,099	(14,203)
Other comprehensive income (loss), net of tax	(11,004)	3,421	(11,933)
Total comprehensive income, net of tax	$ 97,028	$ 90,251	$ 50,188