OTHER COMPREHENSIVE INCOME (LOSS) Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
AFS Debt Securities:
Unrealized holding gains, pre-tax amount	$ (5,163)	$ (53,580)	$ 1,330	$ (146,333)
Unrealized holdings gains, tax (expense) benefit	1,110	11,520	(285)	31,462
Unrealized holdings gains, after-tax amount	(4,053)	(42,060)	1,045	(114,871)
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, pre-tax amount	1,696	0	(3,395)	0
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, tax (expense) benefit	(365)	0	730	0
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, after-tax amount	1,331	0	(2,665)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	0	(9)	0	(9)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	0	2	0	2
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	(7)	0	(7)
Net unrealized gains, pre-tax amount	(6,859)	(53,571)	4,725	(146,324)
Net unrealized gains, tax (expense) benefit	1,475	11,518	(1,015)	31,460
Net unrealized gains, after-tax amount	(5,384)	(42,053)	3,710	(114,864)
Cash Flow Hedges:
Net decrease in fair value, pre-tax amount	3,586	3,588	476	7,223
Net decrease in fair value, tax (expense) benefit	(772)	(771)	(102)	(1,553)
Net decrease in fair value, after-tax amount	2,814	2,817	374	5,670
Net decrease in fair value, pre-tax amount	3,729	3,590	410	7,343
Net decrease in fair value, tax (expense) benefit	(802)	(771)	(88)	(1,579)
Net decrease in fair value, after-tax amount	2,927	2,819	322	5,764
Postretirement Plans:
Net gain on postretirement plans, pre-tax amount	(8)	231	(14)	463
Net gain on postretirement plans, tax (expense) benefit	2	(50)	3	(100)
Net gain on postretirement plans, net of tax	(6)	181	(11)	363
Other comprehensive income, pre-tax amount	(3,138)	(49,750)	5,121	(138,518)
Other comprehensive income, tax (expense) benefit	675	10,697	(1,100)	29,781
Other comprehensive (loss) income	(2,463)	(39,053)	4,021	(108,737)
Interest Expense, Borrowings
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	719	(239)	1,645	(739)
Less: effective portion reclassified into interest expense, tax (expense) benefit	(155)	51	(353)	159
Less: effective portion reclassified into interest expense, after-tax amount	564	(188)	1,292	(580)
Interest Income, Interest and Fees on Loans
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	(862)	237	(1,579)	619
Less: effective portion reclassified into interest expense, tax (expense) benefit	185	(51)	339	(133)
Less: effective portion reclassified into interest expense, after-tax amount	$ (677)	$ 186	$ (1,240)	$ 486