ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Change in unrealized gain (loss) on securities:
Change in net unrealized gain (loss) during the period	$ (33,157)		$ 8,966		$ (103,288)	$ (6,568)
Reclassification adjustment for net gains included in net gain on securities and other assets			(20)			(1,207)
Accretion of net unrealized loss on securities transferred to held to maturity	829				999
Net change	(32,328)		8,946		(102,289)	(7,775)
Tax (benefit) expense	(10,169)		2,817		(32,171)	(2,512)
Net change in unrealized gain (loss) on securities, net of reclassification adjustments and tax	(22,159)		6,129		(70,118)	(5,263)
Change in pension and other postretirement obligations:
Reclassification adjustment for expense included in other expense	(936)		(438)		(1,870)	(860)
Reclassification adjustment for curtailment loss						1,543
Change in the net actuarial gain	998		644		1,995	1,529
Net change	62		206		125	2,212
Tax expense	18		95		39	730
Net change in pension and other postretirement obligations	44		111		86	1,482
Change in unrealized gain (loss) on derivatives:
Change in net unrealized gain (loss) during the period	2,309		(1,406)		9,161	3,542
Reclassification adjustment for loss included in loss on termination of derivatives						16,505
Reclassification adjustment for expense included in interest expense	(54)		10		(23)	864
Net change	2,255		(1,396)		9,138	20,911
Tax (benefit) expense	710		799		2,875	6,630
Net change in unrealized gain (loss) on derivatives, net of reclassification adjustments and tax	1,545		(2,195)		6,263	14,281
Total other comprehensive (loss) income, net of tax	$ (20,570)	$ (43,199)	$ 4,045	$ 6,455	$ (63,769)	$ 10,500