ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassification Adjustments Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment securities gains	$ 2	$ 49	$ 48	$ 178
Interest income	130,422	111,129	350,367	340,213
Recognized actuarial loss	196	228	587	682
Income (loss) before taxes	45,172	76,046	176,594	251,581
Tax expense (benefit)	(11,588)	(19,070)	(44,275)	(61,878)
Net income	$ 33,584	$ 56,976	132,319	189,703
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			48	178
Income (loss) before taxes			48	178
Tax expense (benefit)			(12)	(45)
Net income			36	133
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			(1,735)	0
Income (loss) before taxes			(1,735)	0
Tax expense (benefit)			469	0
Net income			(1,266)	0
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			(587)	(682)
Defined Benefit Pension Plan | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (loss) before taxes			(587)	(682)
Tax expense (benefit)			168	162
Net income			$ (419)	$ (520)