OTHER COMPREHENSIVE INCOME (LOSS) Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AFS Debt Securities:
Unrealized holding gains, pre-tax amount	$ 2,925	$ 9,082	$ (19,380)	$ 33,197
Unrealized holdings gains, tax (expense) benefit	(629)	(1,952)	4,167	(7,137)
Unrealized holdings gains, after-tax amount	2,296	7,130	(15,213)	26,060
Net unrealized gains, pre-tax amount	2,925	9,082	(19,380)	33,197
Net unrealized gains, tax (expense) benefit	(629)	(1,952)	4,167	(7,137)
Net unrealized gains, after-tax amount	2,296	7,130	(15,213)	26,060
Cash Flow Hedges:
Net decrease in fair value, pre-tax amount	(3,203)	39	3,189	(1,110)
Net decrease in fair value, tax (expense) benefit	689	(8)	(685)	239
Net decrease in fair value, after-tax amount	(2,514)	31	2,504	(871)
Less: effective portion reclassified into interest expense, after-tax amount	(150)	(21)	(296)	(169)
Net decrease in fair value, pre-tax amount	(3,011)	66	3,567	(894)
Net decrease in fair value, tax (expense) benefit	647	(14)	(767)	192
Net decrease in fair value, after-tax amount	(2,364)	52	2,800	(702)
Postretirement Plans:
Net actuarial gain, after-tax amount	175	137	350	275
Net gain on postretirement plans, pre-tax amount	217	169	435	339
Net gain on postretirement plans, tax (expense) benefit	(46)	(36)	(94)	(73)
Net gain on postretirement plans, net of tax	171	133	341	266
Other comprehensive income, pre-tax amount	131	9,317	(15,378)	32,642
Other comprehensive income, tax (expense) benefit	(28)	(2,002)	3,306	(7,018)
Other comprehensive income (loss)	103	7,315	(12,072)	25,624
Interest Expense, Borrowings
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	(595)	(274)	(1,173)	(515)
Less: effective portion reclassified into interest expense, tax (expense) benefit	128	59	252	111
Less: effective portion reclassified into interest expense, after-tax amount	(467)	(215)	(921)	(404)
Interest Income, Interest and Fees on Loans
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	403	247	795	299
Less: effective portion reclassified into interest expense, tax (expense) benefit	(86)	(53)	(170)	(64)
Less: effective portion reclassified into interest expense, after-tax amount	$ 317	$ 194	$ 625	$ 235