ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Change in unrealized gain (loss) on securities:
Change in net unrealized gain (loss) during the period	$ (39,692)			$ (8,654)			$ (142,980)	$ (15,222)
Reclassification adjustment for net gains included in net gain on securities and other assets								(1,207)
Accretion of net unrealized loss on securities transferred to held to maturity	1,112						2,111
Net change	(38,580)			(8,654)			(140,869)	(16,429)
Tax (benefit) expense	(12,133)			(2,714)			(44,304)	(5,226)
Net change in unrealized gain (loss) on securities, net of reclassification adjustments and tax	(26,447)			(5,940)			(96,565)	(11,203)
Change in pension and other postretirement obligations:
Reclassification adjustment for expense included in other expense	(935)			(735)			(2,805)	(1,595)
Reclassification adjustment for curtailment loss								1,543
Change in the net actuarial gain	997			941			2,992	2,470
Net change	62			206			187	2,418
Tax expense	20			65			59	795
Net change in pension and other postretirement obligations	42			141			128	1,623
Change in unrealized gain (loss) on derivatives:
Change in net unrealized gain (loss) during the period	5,387			225			14,548	3,767
Reclassification adjustment for loss included in loss on termination of derivatives								16,505
Reclassification adjustment for expense included in interest expense	(546)			38			(569)	902
Net change	4,841			263			13,979	21,174
Tax (benefit) expense	1,522			82			4,397	6,712
Net change in unrealized gain (loss) on derivatives, net of reclassification adjustments and tax	3,319			181			9,582	14,462
Total other comprehensive (loss) income, net of tax	$ (23,086)	$ (20,570)	$ (43,199)	$ (5,618)	$ 4,045	$ 6,455	$ (86,855)	$ 4,882