ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Change in unrealized holding gain or loss on securities available-for-sale [Abstract]
Change in net unrealized gain or loss during the period	$ 2,062	$ (2,770)	$ 10,877	$ (5,637)
Reclassification adjustment for net (gains) losses included in net gain on securities and other assets	(66)	(4)	67	(1,374)
Net change	1,996	(2,774)	10,944	(7,011)
Tax expense (benefit)	600	(767)	3,478	(2,151)
Net change in unrealized holding gain or loss on securities available-for-sale	1,396	(2,007)	7,466	(4,860)
Change in pension and other postretirement obligations [Abstract]
Reclassification adjustment for expense included in other expense	182	162	546	485
Change in the net actuarial gain or loss	55	125	420	243
Net change	237	287	966	728
Tax expense	76	94	310	238
Net change in pension and other postretirement obligations	161	193	656	490
Change in unrealized gain or loss on derivatives:
Change in net unrealized gain or loss during the period	(2,044)	966	(10,717)	3,792
Reclassification adjustment for expense included in interest expense	(279)	(212)	(967)	(462)
Net change	(2,323)	754	(11,684)	3,330
Tax expense (benefit)	(746)	96	(3,754)	932
Net change in unrealized gain or loss on derivatives	(1,577)	658	(7,930)	2,398
Other comprehensive income (loss), net of tax	$ (20)	$ (1,156)	$ 192	$ (1,972)