PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS - SCHEDULE OF COMPONENTS OF NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Amounts recognized in net periodic benefit cost
Service cost	$ 20,878	$ 21,223	$ 20,657
Interest cost	35,756	31,943	40,996
Expected return on plan assets	(54,520)	(58,612)	(57,370)
Amortization of prior service (credit) cost	(7,230)	(7,202)	(5,822)
Amortization of net loss (gain)	32,647	26,875	33,648
Curtailment credit	0	(299)	0
Settlement loss	5,498	20,211	17,732
Total net periodic benefit cost	33,029	34,139	49,841
Change in plan assets and benefit obligations recognized in AOCI, pre-tax
Actuarial net (gain) loss	(52,028)	3,715	(73,768)
Prior service cost (credit)	7,232	7,198	(2,650)
Total recognized in other comprehensive (income) loss, pre-tax	(44,796)	10,913	(76,418)
Net amounts recognized in periodic benefit cost and AOCI	(11,767)	45,052	(26,577)
Other Benefits
Amounts recognized in net periodic benefit cost
Service cost	151	230	263
Interest cost	7,837	6,923	8,837
Expected return on plan assets	0	0	0
Amortization of prior service (credit) cost	811	836	748
Amortization of net loss (gain)	(385)	0	(1)
Curtailment credit	0	0	0
Settlement loss	0	0	0
Total net periodic benefit cost	8,414	7,989	9,847
Change in plan assets and benefit obligations recognized in AOCI, pre-tax
Actuarial net (gain) loss	23,956	(10,771)	2,139
Prior service cost (credit)	(810)	(838)	(744)
Total recognized in other comprehensive (income) loss, pre-tax	23,146	(11,609)	1,395
Net amounts recognized in periodic benefit cost and AOCI	$ 31,560	$ (3,620)	$ 11,242