PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS - PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS NARRATIVE (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) postretirement_plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2025
Defined Benefit Plan Disclosure [Line Items]
Number of Defined Benefit Other Post-retirement Plans and Defined Contribution Other Post-retirement Plans | postretirement_plan	2
Defined Benefit Plan, Accumulated Benefit Obligation	$ 1,123,102	$ 1,063,955
Defined Contribution Plan, Cost	52,793	47,651	$ 47,959
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ (90,140)	$ (89,092)
Discount rate	2.30%	3.10%
Employer contributions	$ 2,862	$ 3,660
Defined Benefit Plans, Minimum Future Employer Contributions in Next Fiscal Year	1,611
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ (15,218)	$ (23,635)
Discount rate	2.50%	3.20%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	6.10%	6.40%
Employer contributions	$ 8,809	$ 16,474
Other Benefits  | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate				5.00%