CHANGE IN ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	$ (24,405)	$ (21,108)	$ (68,825)	$ (63,567)
Income before taxes	100,872	85,517	283,380	262,907
Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	3,301	3,916	9,617	11,294
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net unrealized holding losses on securities transferred between available-for-sale and held-to-maturity:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net unrealized losses to income during the period	4,433	5,217	12,927	15,055
Income taxes	(1,063)	(1,252)	(3,102)	(3,613)
Total reclassifications	3,370	3,965	9,825	11,442
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Prior service credits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credits	(19)	(19)	(57)	(57)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of defined benefit pension plan-related items:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	22	16	66	47
Actuarial gains	(72)	(46)	(217)	(138)
Income before taxes	(91)	(65)	(274)	(195)
Total reclassifications	$ (69)	$ (49)	$ (208)	$ (148)