ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Reclassified out of AOCI) (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Amounts reclassified out of each component of accumulated other comprehensive income
Total reclassification adjustments from AOCI for the period, net of tax	$ 18,714	$ 18,038	$ 9,917	$ 8,326	$ 36,752	$ 18,243
Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Total reclassification adjustments from AOCI for the period, net of tax	(151)		(204)		(335)	(407)
Investment Securities
Amounts reclassified out of each component of accumulated other comprehensive income
Reclassification from AOCI, net of tax	37		0		37	0
Defined Benefit Plans
Amounts reclassified out of each component of accumulated other comprehensive income
Reclassification from AOCI, net of tax	(188)		(204)		(372)	(407)
Defined Benefit Plans | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(276)		(276)		(527)	(553)
Amortization of defined benefit plan items, tax	88		72		155	146
Reclassification from AOCI, net of tax	(188)		(204)		(372)	(407)
Amortization of net actuarial loss
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(272)		(269)		(518)	(537)
Amortization of defined benefit plan items, tax	87		70		153	142
Reclassification from AOCI, net of tax	(185)		(199)		(365)	(395)
Amortization of net actuarial loss | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(272)		(269)		(518)	(537)
Amortization of net transition obligation
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(4)		(4)		(9)	(9)
Amortization of defined benefit plan items, tax	1		1		2	2
Reclassification from AOCI, net of tax	(3)		(3)		(7)	(7)
Amortization of net transition obligation | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(4)		(4)		(9)	(9)
Amortization of prior service cost
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax			(3)			(7)
Amortization of defined benefit plan items, tax			1			2
Reclassification from AOCI, net of tax			(2)			(5)
Amortization of prior service cost | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	$ 0		$ (3)		$ 0	$ (7)