ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning of period	$ 2,545,712	$ 2,418,735
Other comprehensive income (loss), net of tax	(13)	284
Balance, end of period	3,423,041	2,395,312
Total Post-Retirement Benefits Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning of period	884	2,001
Other comprehensive income (loss), net of tax	(13)	284
Balance, end of period	871	2,285
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance, beginning of period	884	2,001
Other comprehensive income (loss), net of tax	(13)	284
Balance, end of period	$ 871	$ 2,285