SEGMENT REPORTING - Other Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Depreciation expense	$ 2,027,413	$ 1,878,929	$ 1,388,570
Amortization expense and other non-cash charges, net	207,746	195,328	155,677
Interest expense (income)	261,342	241,381	180,488
Capital expenditures paid	1,146,521	3,735,174	3,050,409
Total assets	12,931,954	14,475,334	13,347,808
Operating Segments | FMS
Segment Reporting Information [Line Items]
Depreciation expense	1,981,426	1,825,816	1,346,484
Amortization expense and other non-cash charges, net	135,499	128,322	82,980
Interest expense (income)	255,264	243,406	181,335
Capital expenditures paid	1,089,773	3,643,573	2,979,482
Total assets	11,274,450	12,991,716	11,854,454
Operating Segments | SCS
Segment Reporting Information [Line Items]
Depreciation expense	38,652	42,428	34,631
Amortization expense and other non-cash charges, net	68,878	61,419	70,099
Interest expense (income)	602	1,038	1,171
Capital expenditures paid	37,742	49,421	45,348
Total assets	1,313,312	1,236,589	1,123,864
Operating Segments | DTS
Segment Reporting Information [Line Items]
Depreciation expense	2,955	3,795	4,773
Amortization expense and other non-cash charges, net	1,025	1,510	1,545
Interest expense (income)	(3,176)	(3,224)	(2,262)
Capital expenditures paid	1,459	2,182	1,444
Total assets	295,738	327,384	324,906
CSS
Segment Reporting Information [Line Items]
Depreciation expense	4,380	6,890	2,682
Amortization expense and other non-cash charges, net	2,344	4,077	1,053
Interest expense (income)	8,652	161	244
Capital expenditures paid	17,547	39,998	24,135
Total assets	328,329	305,631	404,999
Depreciation expense reallocated to segments	27,000	27,000	25,000
Eliminations
Segment Reporting Information [Line Items]
Depreciation expense	0	0	0
Amortization expense and other non-cash charges, net	0	0	0
Interest expense (income)	0	0	0
Capital expenditures paid	0	0	0
Total assets	$ (279,875)	$ (385,986)	$ (360,415)