ACCUMULATED OTHER COMPREHENSIVE INCOME/ (LOSS) - Reclassification Adjustments Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment securities gains	$ 0	$ 0	$ 0	$ 0
Interest and dividends on investment securities	165,113	158,150	331,127	309,497
Recognized actuarial loss	0	226	0	451
Income before income tax expense	30,748	33,456	58,064	101,940
Tax expense (benefit)	(7,941)	(8,711)	(14,885)	(25,942)
Net income	$ 22,807	$ 24,745	43,179	75,998
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			(736)	(863)
Income before income tax expense			(736)	(863)
Tax expense (benefit)			187	220
Net income			(549)	(643)
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	(451)
Defined Benefit Pension Plan | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense			0	(451)
Tax expense (benefit)			0	115
Net income			$ 0	$ (336)