OTHER COMPREHENSIVE INCOME (LOSS) Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
AFS Debt Securities:
Unrealized holding gains, pre-tax amount	$ (53,580)	$ 2,925	$ (146,333)	$ (19,380)
Unrealized holdings gains, tax (expense) benefit	11,520	(629)	31,462	4,167
Unrealized holdings gains, after-tax amount	(42,060)	2,296	(114,871)	(15,213)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(7)	0	(7)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	2	0	2	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(9)	0	(9)	0
Net unrealized gains, pre-tax amount	(53,571)	2,925	(146,324)	(19,380)
Net unrealized gains, tax (expense) benefit	11,518	(629)	31,460	4,167
Net unrealized gains, after-tax amount	(42,053)	2,296	(114,864)	(15,213)
Cash Flow Hedges:
Net decrease in fair value, pre-tax amount	3,588	(3,203)	7,223	3,189
Net decrease in fair value, tax (expense) benefit	(771)	689	(1,553)	(685)
Net decrease in fair value, after-tax amount	2,817	(2,514)	5,670	2,504
Net decrease in fair value, pre-tax amount	3,590	(3,011)	7,343	3,567
Net decrease in fair value, tax (expense) benefit	(771)	647	(1,579)	(767)
Net decrease in fair value, after-tax amount	2,819	(2,364)	5,764	2,800
Postretirement Plans:
Net gain on postretirement plans, pre-tax amount	231	217	463	435
Net gain on postretirement plans, tax (expense) benefit	(50)	(46)	(100)	(94)
Net gain on postretirement plans, net of tax	181	171	363	341
Other comprehensive income, pre-tax amount	(49,750)	131	(138,518)	(15,378)
Other comprehensive income, tax (expense) benefit	10,697	(28)	29,781	3,306
Other comprehensive (loss) income	(39,053)	103	(108,737)	(12,072)
Interest Expense, Borrowings
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	(239)	(595)	(739)	(1,173)
Less: effective portion reclassified into interest expense, tax (expense) benefit	51	128	159	252
Less: effective portion reclassified into interest expense, after-tax amount	(188)	(467)	(580)	(921)
Interest Income, Interest and Fees on Loans
Cash Flow Hedges:
Less: effective portion reclassified into interest expense, pre-tax amount	237	403	619	795
Less: effective portion reclassified into interest expense, tax (expense) benefit	(51)	(86)	(133)	(170)
Less: effective portion reclassified into interest expense, after-tax amount	$ 186	$ 317	$ 486	$ 625