CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 96,070	$ 81,051	$ 65,384
Other comprehensive income (loss) net of tax:
Unrealized holding gain (loss) on securities available for sale arising during the period, net of tax of $5,193, $4,893, and $20	9,645	(9,087)	(37)
Unrealized gain (loss) on cash flow hedges arising during the period, net of tax of $4, $128, and $588	9	(240)	(1,093)
Reclassification adjustment for net gains included in net income net of tax of $576, $749, and $435	(1,070)	(1,390)	(808)
Defined benefit pension plans, net of tax of $1,125, $809, and $1,187
Net gain (loss) arising during period	2,686	(470)	2,404
Amortization of prior service cost	(597)	(1,032)	(198)
Period change	10,673	(12,219)	268
Comprehensive income	$ 106,743	$ 68,832	$ 65,652