PENSION AND OTHER POSTRETIREMENT BENEFITS - Schedule of Defined Benefit Plans Disclosure (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 1,591	$ 1,688	$ 3,182	$ 3,375
Interest Cost	3,236	3,763	6,472	7,526
Expected Return on Plan Assets	(5,834)	(5,452)	(11,668)	(10,904)
Amortizations:
Prior Service Cost	25	26	50	53
Actuarial Loss	3,194	2,715	6,388	5,430
Net Periodic Benefit Cost	2,212	2,740	4,424	5,480
Capitalized Benefit Cost	(566)	(517)	(1,132)	(1,061)
Deferred Benefit Cost	(316)	(408)	(632)	(816)
Total Net Periodic Benefit Expense	1,330	1,815	2,660	3,603
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	212	165	424	329
Interest Cost	475	608	950	1,216
Expected Return on Plan Assets	(1,436)	(1,346)	(2,872)	(2,691)
Amortizations:
Prior Service Cost	(156)	(144)	(312)	(288)
Actuarial Loss	273	193	546	385
Net Periodic Benefit Cost	(632)	(524)	(1,264)	(1,049)
Capitalized Benefit Cost	(106)	(106)	(212)	(214)
Deferred Benefit Cost	336	396	673	792
Total Net Periodic Benefit Expense	$ (402)	$ (234)	$ (803)	$ (471)