ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 2,122,448	$ 1,807,633	$ 2,034,770	$ 1,912,571
Other comprehensive income (loss) before reclassifications			18,834	(253,481)
Amounts reclassified from accumulated other comprehensive income			2,353	(188)
Period change	(19,050)	(114,164)	21,187	(253,669)
Ending balance	2,145,565	1,977,641	2,145,565	1,977,641
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(198,914)	(84,392)	(239,151)	55,113
Period change	(19,050)	(114,164)	21,187	(253,669)
Ending balance	(217,964)	(198,556)	(217,964)	(198,556)
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			18,924	(253,807)
Amounts reclassified from accumulated other comprehensive income			2,341	(518)
Period change			21,265	(254,325)
Ending balance	(213,230)	(194,551)	(213,230)	(194,551)
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance			130	(660)
Other comprehensive income (loss) before reclassifications			(90)	326
Amounts reclassified from accumulated other comprehensive income			12	330
Period change			(78)	656
Ending balance	52	(4)	52	(4)
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)	$ (4,786)	$ (4,001)