OTHER COMPREHENSIVE INCOME (LOSS) Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AFS Debt Securities:
Unrealized holding gains, pre-tax amount	$ (6,546)	$ (746)	$ (25,926)	$ 32,451
Unrealized holdings gains, tax (expense) benefit	1,407	160	5,574	(6,977)
Unrealized holdings gains, after-tax amount	(5,139)	(586)	(20,352)	25,474
Net unrealized gains, pre-tax amount	(6,546)	(746)	(25,926)	32,451
Net unrealized gains, tax (expense) benefit	1,407	160	5,574	(6,977)
Net unrealized gains, after-tax amount	(5,139)	(586)	(20,352)	25,474
Cash Flow Hedges:
Net decrease in fair value, pre-tax amount	466	688	3,655	(418)
Net decrease in fair value, tax (expense) benefit	(100)	(148)	(785)	90
Net decrease in fair value, after-tax amount	366	540	2,870	(328)
Net decrease in fair value, pre-tax amount	595	856	4,162	(38)
Net decrease in fair value, tax (expense) benefit	(128)	(184)	(895)	8
Net decrease in fair value, after-tax amount	467	672	3,267	(30)
Postretirement Plans:
Net gain on postretirement plans, pre-tax amount	217	169	652	508
Net gain on postretirement plans, tax (expense) benefit	(46)	(36)	(140)	(109)
Net gain on postretirement plans, net of tax	171	133	512	399
Other comprehensive income, pre-tax amount	(5,734)	279	(21,112)	32,921
Other comprehensive income, tax (expense) benefit	1,233	(60)	4,539	(7,078)
Other comprehensive (loss) income	(4,501)	219	(16,573)	25,843
Interest Expense, Borrowings
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	(539)	(479)	(1,712)	(990)
Less: effective portion reclassified into interest expense, tax (expense) benefit	116	103	368	213
Less: effective portion reclassified into interest expense, after-tax amount	(423)	(376)	(1,344)	(777)
Interest Income, Interest and Fees on Loans
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	410	311	1,205	610
Less: effective portion reclassified into interest expense, tax (expense) benefit	(88)	(67)	(258)	(131)
Less: effective portion reclassified into interest expense, after-tax amount	$ 322	$ 244	$ 947	$ 479