REVENUE Disaggregation of Revenue - Geographical (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 2,221,622	$ 2,161,306
United States
Disaggregation of Revenue [Line Items]
Revenues	1,983,062	1,917,639
Canada
Disaggregation of Revenue [Line Items]
Revenues	122,158	119,346
Europe
Disaggregation of Revenue [Line Items]
Revenues	67,088	71,951
Mexico
Disaggregation of Revenue [Line Items]
Revenues	49,314	52,370
SCS
Disaggregation of Revenue [Line Items]
Revenues	706,700	628,447
Operating Segments | FMS
Disaggregation of Revenue [Line Items]
Revenues	1,335,485	1,340,237
Operating Segments | FMS | United States
Disaggregation of Revenue [Line Items]
Revenues	1,197,984	1,197,521
Operating Segments | FMS | Canada
Disaggregation of Revenue [Line Items]
Revenues	70,413	70,765
Operating Segments | FMS | Europe
Disaggregation of Revenue [Line Items]
Revenues	67,088	71,951
Operating Segments | FMS | Mexico
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | SCS
Disaggregation of Revenue [Line Items]
Revenues	706,700	628,447
Operating Segments | SCS | United States
Disaggregation of Revenue [Line Items]
Revenues	601,298	522,525
Operating Segments | SCS | Canada
Disaggregation of Revenue [Line Items]
Revenues	56,088	53,552
Operating Segments | SCS | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | SCS | Mexico
Disaggregation of Revenue [Line Items]
Revenues	49,314	52,370
Operating Segments | DTS
Disaggregation of Revenue [Line Items]
Revenues	320,507	334,888
Operating Segments | DTS | United States
Disaggregation of Revenue [Line Items]
Revenues	320,507	334,888
Operating Segments | DTS | Canada
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | DTS | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | DTS | Mexico
Disaggregation of Revenue [Line Items]
Revenues	0	0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(141,070)	(142,266)
Eliminations | United States
Disaggregation of Revenue [Line Items]
Revenues	(136,727)	(137,295)
Eliminations | Canada
Disaggregation of Revenue [Line Items]
Revenues	(4,343)	(4,971)
Eliminations | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Eliminations | Mexico
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0