REVENUE Disaggregation of Revenue - Geographical (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,180,327	$ 1,904,205
United States
Disaggregation of Revenue [Line Items]
Total revenue	1,926,794	1,658,583
Canada
Disaggregation of Revenue [Line Items]
Total revenue	118,321	113,095
Europe
Disaggregation of Revenue [Line Items]
Total revenue	78,642	82,796
Mexico
Disaggregation of Revenue [Line Items]
Total revenue	53,277	44,032
Singapore
Disaggregation of Revenue [Line Items]
Total revenue	3,293	5,699
FMS
Disaggregation of Revenue [Line Items]
Total revenue	1,195,035	1,110,528
DTS
Disaggregation of Revenue [Line Items]
Total revenue	349,621	298,970
SCS
Disaggregation of Revenue [Line Items]
Total revenue	635,671	494,707
Operating Segments | FMS
Disaggregation of Revenue [Line Items]
Total revenue	1,351,599	1,243,050
Operating Segments | FMS | United States
Disaggregation of Revenue [Line Items]
Total revenue	1,198,943	1,085,446
Operating Segments | FMS | Canada
Disaggregation of Revenue [Line Items]
Total revenue	74,014	74,808
Operating Segments | FMS | Europe
Disaggregation of Revenue [Line Items]
Total revenue	78,642	82,796
Operating Segments | FMS | Mexico
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | FMS | Singapore
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | DTS
Disaggregation of Revenue [Line Items]
Total revenue	349,621	298,970
Operating Segments | DTS | United States
Disaggregation of Revenue [Line Items]
Total revenue	349,621	298,970
Operating Segments | DTS | Canada
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | DTS | Europe
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | DTS | Mexico
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | DTS | Singapore
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | SCS
Disaggregation of Revenue [Line Items]
Total revenue	635,671	494,707
Operating Segments | SCS | United States
Disaggregation of Revenue [Line Items]
Total revenue	529,393	401,883
Operating Segments | SCS | Canada
Disaggregation of Revenue [Line Items]
Total revenue	49,708	43,093
Operating Segments | SCS | Europe
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Operating Segments | SCS | Mexico
Disaggregation of Revenue [Line Items]
Total revenue	53,277	44,032
Operating Segments | SCS | Singapore
Disaggregation of Revenue [Line Items]
Total revenue	3,293	5,699
Eliminations
Disaggregation of Revenue [Line Items]
Total revenue	(156,564)	(132,522)
Eliminations | United States
Disaggregation of Revenue [Line Items]
Total revenue	(151,163)	(127,716)
Eliminations | Canada
Disaggregation of Revenue [Line Items]
Total revenue	(5,401)	(4,806)
Eliminations | Europe
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Eliminations | Mexico
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Eliminations | Singapore
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Eliminations | FMS
Disaggregation of Revenue [Line Items]
Total revenue	156,564	132,522
Eliminations | DTS
Disaggregation of Revenue [Line Items]
Total revenue	0	0
Eliminations | SCS
Disaggregation of Revenue [Line Items]
Total revenue	$ 0	$ 0