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OPERATING SEGMENT DATA - (Concentrations) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues | Customer concentration risk | Asset-Based and ArcBest segments | FleetNet
Concentrations
Concentration Risk, Percentage	18.00%	19.00%	20.00%	17.00%

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