ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Change in unrealized gain or loss on securities:
Change in net unrealized gain (loss) during the period	$ (70,131)	$ (15,534)
Reclassification adjustment for net gains included in net gain on securities and other assets		(1,187)
Accretion of net unrealized loss on securities transferred to held to maturity	170
Net change	(69,961)	(16,721)
Tax benefit	(22,002)	(5,329)
Net change in unrealized gain or loss on securities, net of reclassification adjustments and tax	(47,959)	(11,392)
Change in pension and other postretirement obligations:
Reclassification adjustment for expense included in other expense	(934)	(422)
Reclassification adjustment for curtailment loss		1,543
Change in the net actuarial gain or loss	997	885
Net change	63	2,006
Tax expense	21	635
Net change in pension and other postretirement obligations	42	1,371
Change in unrealized gain or loss on derivatives:
Change in net unrealized gain or loss during the period	6,852	4,948
Reclassification adjustment for loss included in loss on termination of derivatives		16,505
Reclassification adjustment for expense included in interest expense	31	854
Net change	6,883	22,307
Tax benefit	2,165	5,831
Net change in unrealized gain or loss on derivatives, net of reclassification adjustments and tax	4,718	16,476
Total other comprehensive (loss) income, net of tax	$ (43,199)	$ 6,455