GOODWILL AND OTHER INTANGIBLE ASSETS - Change in the Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance, beginning of year	$ 1,232,796	$ 1,108,337
Acquisitions	28,591	132,797
Translation	14,429	(8,338)
Balance, end of year	1,275,816	1,232,796
NAST
Goodwill [Roll Forward]
Balance, beginning of year	907,230	815,639
Acquisitions	3,673	97,727
Translation	10,583	(6,136)
Balance, end of year	921,486	907,230
Global Forwarding
Goodwill [Roll Forward]
Balance, beginning of year	159,050	142,993
Acquisitions	24,918	17,133
Translation	1,905	(1,076)
Balance, end of year	185,873	159,050
Robinson Fresh
Goodwill [Roll Forward]
Balance, beginning of year	139,558	125,469
Acquisitions	0	15,033
Translation	1,627	(944)
Balance, end of year	141,185	139,558
All Other and Corporate
Goodwill [Roll Forward]
Balance, beginning of year	26,958	24,236
Acquisitions	0	2,904
Translation	314	(182)
Balance, end of year	$ 27,272	$ 26,958