ACCUMULATED OTHER COMPREHENSIVE LOSS - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 2,145,565	$ 1,977,641	$ 2,034,770	$ 1,912,571
Other comprehensive loss before reclassifications			(71,775)	(368,696)
Amounts reclassified from accumulated other comprehensive income			3,656	(506)
Period change	(89,306)	(115,533)	(68,119)	(369,202)
Ending balance	2,092,644	1,906,666	2,092,644	1,906,666
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(217,964)	(198,556)	(239,151)	55,113
Period change	(89,306)	(115,533)	(68,119)	(369,202)
Ending balance	(307,270)	(314,089)	(307,270)	(314,089)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Beginning balance			(234,495)	59,774
Other comprehensive loss before reclassifications			(71,633)	(369,096)
Amounts reclassified from accumulated other comprehensive income			3,644	(898)
Period change			(67,989)	(369,994)
Ending balance	(302,484)	(310,220)	(302,484)	(310,220)
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance			130	(660)
Other comprehensive loss before reclassifications			(142)	400
Amounts reclassified from accumulated other comprehensive income			12	392
Period change			(130)	792
Ending balance	0	132	0	132
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance			(4,786)	(4,001)
Other comprehensive loss before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income			0	0
Period change			0	0
Ending balance	$ (4,786)	$ (4,001)	$ (4,786)	$ (4,001)