ACCUMULATED OTHER COMPREHENSIVE INCOME/ (LOSS) - Reclassification Adjustments Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment securities gains	$ 0	$ 0
Interest and dividends on investment securities	166,014	151,347
Recognized actuarial loss	0	225
Income before income tax expense	27,316	68,484
Tax expense (benefit)	(6,944)	(17,231)
Net income	20,372	51,253
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	0
Income before income tax expense	0	0
Tax expense (benefit)	0	0
Net income	0	0
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	(371)	(405)
Income before income tax expense	(371)	(405)
Tax expense (benefit)	94	103
Net income	(277)	(302)
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	0	(225)
Defined Benefit Pension Plan | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	0	(225)
Tax expense (benefit)	0	57
Net income	$ 0	$ (168)