ACCUMULATED OTHER COMPREHENSIVE LOSS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 2,247,713	$ 2,034,770
Other comprehensive income (loss) before reclassifications	(22,061)	38,997
Amounts reclassified from accumulated other comprehensive income (loss)	2	1,240
Period change	(22,059)	40,237
Ending balance	2,224,803	2,122,448
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(175,970)	(239,151)
Period change	(22,059)	40,237
Ending balance	(198,029)	(198,914)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(173,654)	(234,495)
Other comprehensive income (loss) before reclassifications	(22,061)	39,038
Amounts reclassified from accumulated other comprehensive income (loss)	2	1,241
Period change	(22,059)	40,279
Ending balance	(195,713)	(194,216)
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance	0	130
Other comprehensive income (loss) before reclassifications	0	(41)
Amounts reclassified from accumulated other comprehensive income (loss)	0	(1)
Period change	0	(42)
Ending balance	0	88
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(2,316)	(4,786)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Period change	0	0
Ending balance	$ (2,316)	$ (4,786)