ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Change in unrealized gain (loss) on securities:
Change in net unrealized loss during the period	$ (11,291)		$ (33,157)		$ (13,593)	$ (103,288)
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	796		829		1,553	999
Net change	(10,495)		(32,328)		(10,593)	(102,289)
Tax benefit (expense)	(3,109)		(10,169)		(445)	(32,171)
Net change in unrealized loss on securities, net of reclassification adjustments and tax	(7,386)		(22,159)		(10,148)	(70,118)
Change in pension and other postretirement obligations:
Reclassification adjustment for expense included in other expense	(370)		(936)		(740)	(1,870)
Change in the net actuarial gain	814		998		1,035	1,995
Net change	444		62		295	125
Tax (expense) benefit	131		18		87	39
Net change in pension and other postretirement obligations	313		44		208	86
Change in unrealized gain (loss) on derivatives:
Change in net unrealized gain (loss) during the period	1,586		2,309		(525)	9,161
Reclassification adjustment for expense included in interest expense	299		(54)		(14)	(23)
Net change	1,885		2,255		(539)	9,138
Tax (expense) benefit	559		710		(473)	2,875
Net change in unrealized (loss) gain on derivatives, net of reclassification adjustments and tax	1,326		1,545		(66)	6,263
Other comprehensive loss, net of tax	$ (5,747)	$ (4,259)	$ (20,570)	$ (43,199)	$ (10,006)	$ (63,769)