CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income		$ 57,330	$ 52,084	$ 46,367
Change in securities available for sale:
Unrealized holding gain (loss) on securities available for sale arising during the period		2,245	(7,238)	(2,720)
Reclassification adjustment for (gains)/losses included in net income		(32)	(66)	(42)
Net securities gain (loss) activity during the period		2,213	(7,304)	(2,762)
Tax effect		(707)	2,746	1,131
Net of tax amount		1,506	(4,558)	(1,631)
Defined benefit pension plans:
Net gain(loss) on defined benefit pension plans		97	(151)	(325)
Amortization of net actuarial loss	[1]	265	215	244
Net gain (loss) activity during the period		362	64	(81)
Tax effect		(151)	(35)	24
Net of tax amount		211	29	(57)
Total other comprehensive income (loss), net of tax		1,717	(4,529)	(1,688)
Comprehensive income		$ 59,047	$ 47,555	$ 44,679

[1] Included in the computation of net pension plan expense as more fully discussed in Note 11.