OTHER COMPREHENSIVE INCOME (LOSS) Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
AFS Debt Securities:
Unrealized holding gains, pre-tax amount	$ 9,885	$ (92,753)
Unrealized holdings gains, tax (expense) benefit	(2,125)	19,942
Unrealized holdings gains, after-tax amount	7,760	(72,811)
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, pre-tax amount	(1,699)	0
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, tax (expense) benefit	365	0
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, after-tax amount	(1,334)	0
Net unrealized gains, pre-tax amount	11,584	(92,753)
Net unrealized gains, tax (expense) benefit	(2,490)	19,942
Net unrealized gains, after-tax amount	9,094	(72,811)
Cash Flow Hedges:
Net decrease in fair value, pre-tax amount	(3,109)	3,635
Net decrease in fair value, tax (expense) benefit	668	(782)
Net decrease in fair value, after-tax amount	(2,441)	2,853
Net decrease in fair value, pre-tax amount	(3,318)	3,753
Net decrease in fair value, tax (expense) benefit	713	(808)
Net decrease in fair value, after-tax amount	(2,605)	2,945
Postretirement Plans:
Net gain on postretirement plans, pre-tax amount	(6)	232
Net gain on postretirement plans, tax (expense) benefit	1	(50)
Net gain on postretirement plans, net of tax	(5)	182
Other comprehensive income, pre-tax amount	8,260	(88,768)
Other comprehensive income, tax (expense) benefit	(1,776)	19,084
Other comprehensive income (loss)	6,484	(69,684)
Interest Expense, Borrowings
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	926	(500)
Less: effective portion reclassified into interest expense, tax (expense) benefit	(199)	108
Less: effective portion reclassified into interest expense, after-tax amount	727	(392)
Interest Income, Interest and Fees on Loans
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	(717)	382
Less: effective portion reclassified into interest expense, tax (expense) benefit	154	(82)
Less: effective portion reclassified into interest expense, after-tax amount	$ (563)	$ 300