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	$ 81,051	$ 65,384	$ 60,162
Other comprehensive income (loss) net of tax:
Unrealized holding gain (loss) on securities available for sale arising during the period, net of tax of $4,893, $20, and $8,001	(9,087)	(37)	14,860
Unrealized gain on securities available for sale for which a portion of an other than temporary impairment has been recognized in income, net of tax of $0, $0, and $995			1,847
Unrealized loss on cash flow hedges arising during the period, net of tax of $128, $588, and $1,397	(240)	(1,093)	(2,599)
Reclassification adjustment for net gains included in net income net of tax of $749, $435, and $760	(1,390)	(808)	(1,410)
Defined benefit pension plans, net of tax of $809, $1,187, and $4,264
Net gain (loss) arising during period	(470)	2,404	(7,580)
Amortization of prior service cost	(1,032)	(198)	(338)
Period change	(12,219)	268	4,780
Comprehensive income	$ 68,832	$ 65,652	$ 64,942