SEGMENT REPORTING - Reportable Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) employee	Sep. 30, 2019 USD ($) employee	Sep. 30, 2020 USD ($) employee	Sep. 30, 2019 USD ($) employee	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Total revenues	$ 4,224,800	$ 3,856,132	$ 11,657,654	$ 11,516,182
Net revenues	589,273	633,431	1,771,679	2,007,447
Income (loss) from operations	168,239	201,085	466,466	653,170
Depreciation and amortization	26,916	25,480	77,067	75,122
Total assets	$ 5,074,838	$ 4,636,549	$ 5,074,838	$ 4,636,549	$ 4,641,060
Average headcount (employee) | employee	14,904	15,782	15,177	15,582
Operating Segments | NAST
Segment Reporting Information [Line Items]
Total revenues	$ 2,923,842	$ 2,826,308	$ 8,222,879	$ 8,495,145
Net revenues	367,943	433,760	1,120,277	1,406,728
Income (loss) from operations	122,526	176,200	357,898	592,215
Depreciation and amortization	7,095	5,734	19,550	18,124
Total assets	$ 3,041,974	$ 2,649,259	$ 3,041,974	$ 2,649,259
Average headcount (employee) | employee	6,702	7,448	6,870	7,436
Operating Segments | Global Forwarding
Segment Reporting Information [Line Items]
Total revenues	$ 831,957	$ 597,695	$ 2,070,161	$ 1,727,745
Net revenues	157,657	135,815	448,931	404,987
Income (loss) from operations	46,299	24,676	117,033	65,497
Depreciation and amortization	9,385	9,186	27,740	27,427
Total assets	$ 1,148,118	$ 995,137	$ 1,148,118	$ 995,137
Average headcount (employee) | employee	4,607	4,790	4,716	4,748
Operating Segments | All Other and Corporate
Segment Reporting Information [Line Items]
Total revenues	$ 469,001	$ 432,129	$ 1,364,614	$ 1,293,292
Net revenues	63,673	63,856	202,471	195,732
Income (loss) from operations	(586)	209	(8,465)	(4,542)
Depreciation and amortization	10,436	10,560	29,777	29,571
Total assets	$ 884,746	$ 992,153	$ 884,746	$ 992,153
Average headcount (employee) | employee	3,595	3,544	3,591	3,398