PENSION AND OTHER POSTRETIREMENT BENEFITS - Schedule of Defined Benefit Plans Disclosure (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 1,591	$ 1,688
Interest Cost	3,236	3,763
Expected Return on Plan Assets	(5,834)	(5,452)
Amortizations:
Prior Service Cost	25	26
Actuarial Loss	3,194	2,715
Net Periodic Benefit Cost	2,212	2,740
Capitalized Benefit Cost	(566)	(544)
Deferred Benefit Cost	(316)	(408)
Total Net Periodic Benefit Expense	1,330	1,788
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	212	165
Interest Cost	475	608
Expected Return on Plan Assets	(1,436)	(1,346)
Amortizations:
Prior Service Cost	(156)	(144)
Actuarial Loss	273	192
Net Periodic Benefit Cost	(632)	(525)
Capitalized Benefit Cost	(106)	(108)
Deferred Benefit Cost	337	396
Total Net Periodic Benefit Expense	$ (401)	$ (237)