ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassification Adjustments Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment securities gains	$ 0	$ 8
Interest income	151,347	106,036
Recognized actuarial loss	225	196
Income (loss) before taxes	68,484	58,264
Tax expense (benefit)	(17,231)	(14,329)
Net income	51,253	43,935
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	8
Income (loss) before taxes	0	8
Tax expense (benefit)	0	(2)
Net income	0	6
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 income	(405)	(319)
Income (loss) before taxes	(405)	(319)
Tax expense (benefit)	103	82
Net income	(302)	(237)
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	(225)	(196)
Defined Benefit Pension Plan | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (loss) before taxes	(225)	(196)
Tax expense (benefit)	57	50
Net income	$ (168)	$ (146)