ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Change in unrealized gain (loss) on securities:
Change in net unrealized loss during the period	$ (2,302)	$ (70,131)
Reclassification adjustment for net losses included in net loss on sale of securities and other assets	1,447
Accretion of net unrealized loss on securities transferred to held-to-maturity	757	170
Net change	(98)	(69,961)
Tax benefit (expense)	2,664	(22,002)
Net change in unrealized loss on securities, net of reclassification adjustments and tax	(2,762)	(47,959)
Change in pension and other postretirement obligations:
Reclassification adjustment for expense included in other expense	(370)	(934)
Change in the net actuarial gain	221	997
Net change	(149)	63
Tax (expense) benefit	(44)	21
Net change in pension and other postretirement obligations	(105)	42
Change in unrealized gain (loss) on derivatives:
Change in net unrealized (loss) gain during the period	(2,111)	6,852
Reclassification adjustment for expense included in interest expense	(313)	31
Net change	(2,424)	6,883
Tax (expense) benefit	(1,032)	2,165
Net change in unrealized (loss) gain on derivatives, net of reclassification adjustments and tax	(1,392)	4,718
Other comprehensive loss, net of tax	$ (4,259)	$ (43,199)