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OPERATING SEGMENT DATA - (Concentrations) (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues | Customer concentration risk | Asset-Based and ArcBest segments | FleetNet
Concentrations
Concentration Risk, Percentage	17.00%	6.00%	2.00%

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