OTHER COMPREHENSIVE INCOME (LOSS), Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in unrealized holding loss on securities transferred to held-to-maturity [Abstract]
Accretion (Amortization) of previously recognized non-credit component of OTTI	$ 20	$ 34	$ (9)
Change in unrealized loss on securities transferred to held-to-maturity	50	51	125
Reclassification adjustment for net gain included in net gain on securities and other assets	1,229	0	0
Net change	1,299	85	116
Tax expense	586	38	50
Net change in unrealized holding loss on securities held-to-maturity and transferred securities	713	47	66
Change in unrealized holding gain on securities available-for-sale [Abstract]
Change in net unrealized gain during the period	551	56	(176)
Reclassification adjustment for net losses (gains) included in net gain on securities and other assets	36	0	(1,384)
Net change	587	56	(1,560)
Tax expense (benefit)	260	26	(702)
Net change in unrealized holding gain on securities available-for-sale	327	30	(858)
Change in pension and other postretirement obligations [Abstract]
Reclassification adjustment for expense included in salaries and employee benefits expense	1,421	1,841	1,890
Change in the net actuarial gain or loss	1,337	0	(901)
Net change	2,758	1,841	989
Tax expense	1,239	832	451
Net change in pension and other postretirement obligations	1,519	1,009	538
Change in unrealized loss on derivatives asset [Abstract]
Change in net unrealized loss during the period	511	3,205	0
Reclassification adjustment for expense included in interest expense	283	23	0
Net change	794	3,228	0
Tax expense	342	1,452	0
Net change in unrealized loss on derivatives asset	452	1,776	0
Other comprehensive income (loss), net of tax	$ 3,011	$ 2,862	$ (254)