ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 2,034,770	$ 1,912,571
Other comprehensive income (loss) before reclassifications	38,997	(139,248)
Amounts reclassified from accumulated other comprehensive income	1,240	(257)
Period change	40,237	(139,505)
Ending balance	2,122,448	1,807,633
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(239,151)	55,113
Period change	40,237	(139,505)
Ending balance	(198,914)	(84,392)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(234,495)	59,774
Other comprehensive income (loss) before reclassifications	39,038	(139,487)
Amounts reclassified from accumulated other comprehensive income	1,241	(447)
Period change	40,279	(139,934)
Ending balance	(194,216)	(80,160)
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance	130	(660)
Other comprehensive income (loss) before reclassifications	(41)	239
Amounts reclassified from accumulated other comprehensive income	(1)	190
Period change	(42)	429
Ending balance	88	(231)
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(4,786)	(4,001)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	0
Period change	0	0
Ending balance	$ (4,786)	$ (4,001)