ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in unrealized gain (loss) on securities:
Change in net unrealized gain (loss) during the period	$ 10,355	$ (138,630)	$ (28,865)
Reclassification adjustment for net losses included in net loss on sale of securities and other assets	1,447		(1,207)
Accretion of net unrealized loss on securities transferred to held-to-maturity	3,142	2,953
Net change	14,944	(135,677)	(30,072)
Tax expense (benefit)	4,316	(42,671)	(9,514)
Net change in unrealized gain (loss) on securities, net of reclassification adjustments and tax	10,628	(93,006)	(20,558)
Change in pension and other postretirement obligations:
Reclassification adjustment for expense included in other expense	(1,547)	(3,715)	(1,092)
Reclassification adjustment for curtailment loss			1,543
Change in the net actuarial (loss) gain	(190)	(2,062)	6,563
Net change	(1,737)	(5,777)	7,014
Tax (benefit) expense	(573)	(1,817)	2,234
Net change in pension and other postretirement obligations	(1,164)	(3,960)	4,780
Change in unrealized gain (loss) on derivatives:
Change in net unrealized (loss) gain during the period	(11,782)	14,412	5,277
Reclassification adjustment for loss included in loss on termination of derivatives			(16,505)
Reclassification adjustment for expense included in interest expense	2,092	(1,621)	940
Net change	(9,690)	12,791	22,722
Tax expense (benefit)	(3,026)	4,023	7,201
Net change in unrealized gain (loss) on derivatives, net of reclassification adjustments and tax	(6,664)	8,768	15,521
Total other comprehensive income (loss), net of tax	$ 2,800	$ (88,198)	$ (257)