CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Net Income	$ 51,882	$ 72,514	$ 44,772
Other comprehensive income:
Change in unrealized holding loss on securities transferred to held-to-maturity	1,299	85	116
Change in unrealized holding loss (gain) on securities available-for-sale	587	56	(1,560)
Change in pension and other postretirement obligations	2,758	1,841	989
Change in unrealized gain on derivative asset	794	3,228	0
Other comprehensive gain (loss) before income taxes	5,438	5,210	(455)
Deferred tax expense (benefit)	2,427	2,348	(201)
Other comprehensive income (loss), net of tax	3,011	2,862	(254)
Total comprehensive income	$ 54,893	$ 75,376	$ 44,518