EMPLOYEE BENEFIT PLANS - Fair Value of Pension Plan Assets (Details) - Pension Plans - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,303,996	$ 1,978,708	$ 1,725,543
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,180,856	1,860,490
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123,140	118,218	$ 121,836
U.S. common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	371,893	384,739
U.S. common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	371,893	384,739
U.S. common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	263,023	379,717
Foreign common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	263,023	379,717
Foreign common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	98,715	84,519
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	98,715	84,519
Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,447,225	1,011,515
Common collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,447,225	1,011,515
Common collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity and hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123,140	118,218
Private equity and hedge funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity and hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity and hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 123,140	$ 118,218