REVENUE FROM CONTRACTS WITH CUSTOMERS - Total Revenues Disaggregated by Major Service Line and Timing of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 3,805,008	$ 3,751,210
Operating Segments | NAST
Disaggregation of Revenue [Line Items]
Total revenues	2,823,745	2,796,784
Operating Segments | Global Forwarding
Disaggregation of Revenue [Line Items]
Total revenues	530,384	537,567
Operating Segments | All Other and Corporate
Disaggregation of Revenue [Line Items]
Total revenues	450,879	416,859
Transportation and logistics services
Disaggregation of Revenue [Line Items]
Total revenues	3,542,118	3,504,932
Transportation and logistics services | Performance obligations completed over time
Disaggregation of Revenue [Line Items]
Total revenues	3,542,118	3,504,932
Transportation and logistics services | Operating Segments | NAST | Performance obligations completed over time
Disaggregation of Revenue [Line Items]
Total revenues	2,823,745	2,796,784
Transportation and logistics services | Operating Segments | Global Forwarding | Performance obligations completed over time
Disaggregation of Revenue [Line Items]
Total revenues	530,384	537,567
Transportation and logistics services | Operating Segments | All Other and Corporate | Performance obligations completed over time
Disaggregation of Revenue [Line Items]
Total revenues	187,989	170,581
Sourcing
Disaggregation of Revenue [Line Items]
Total revenues	262,890	246,278
Sourcing | Performance obligations completed at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	262,890	246,278
Sourcing | Operating Segments | NAST | Performance obligations completed at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Sourcing | Operating Segments | Global Forwarding | Performance obligations completed at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Sourcing | Operating Segments | All Other and Corporate | Performance obligations completed at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	$ 262,890	$ 246,278