ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassification Adjustments Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment securities gains	$ 0	$ 38	$ 0	$ 46
Interest and dividends on investment securities	158,150	113,909	309,497	219,945
Recognized actuarial loss	226	195	451	391
Income (loss) before taxes	33,456	73,158	101,940	131,422
Tax expense (benefit)	(8,711)	(18,358)	(25,942)	(32,687)
Net income	$ 24,745	$ 54,800	75,998	98,735
Unrealized Gains/(Losses) on Debt Securities Available-for-Sale | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment securities gains			0	46
Income (loss) before taxes			0	46
Tax expense (benefit)			0	(12)
Net income			0	34
Unrealized Losses on Debt Securities Transferred from Available-for-Sale to Held-to-Maturity | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and dividends on investment securities			(863)	(1,122)
Income (loss) before taxes			(863)	(1,122)
Tax expense (benefit)			220	288
Net income			(643)	(834)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Recognized actuarial loss			(451)	(391)
Defined Benefit Pension Plan | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (loss) before taxes			(451)	(391)
Tax expense (benefit)			115	100
Net income			$ (336)	$ (291)