ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 1,977,641	$ 1,871,800	$ 1,912,571	$ 1,875,645
Other comprehensive income (loss) before reclassifications			(368,696)	(31,362)
Amounts reclassified from accumulated other comprehensive income			(506)	(3,585)
Period change	(115,533)	(20,191)	(369,202)	(34,947)
Ending balance	1,906,666	1,868,090	1,906,666	1,868,090
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(198,556)	60,080	55,113	74,836
Period change	(115,533)	(20,191)	(369,202)	(34,947)
Ending balance	(314,089)	39,889	(314,089)	39,889
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Beginning balance			59,774	87,988
Other comprehensive income (loss) before reclassifications			(369,096)	(31,379)
Amounts reclassified from accumulated other comprehensive income			(898)	(4,200)
Period change			(369,994)	(35,579)
Ending balance	(310,220)	52,409	(310,220)	52,409
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance			(660)	(1,594)
Other comprehensive income (loss) before reclassifications			400	17
Amounts reclassified from accumulated other comprehensive income			392	615
Period change			792	632
Ending balance	132	(962)	132	(962)
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance			(4,001)	(11,558)
Other comprehensive income (loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income			0	0
Period change			0	0
Ending balance	$ (4,001)	$ (11,558)	$ (4,001)	$ (11,558)