Restructuring, Impairment and Other Costs - Restructuring Costs by Segment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ (600)	$ 639	$ 0	$ (5,264)
Trucking
Restructuring Cost and Reserve [Line Items]
Costs incurred		587	0	(4,848)
USAT Logistics
Restructuring Cost and Reserve [Line Items]
Costs incurred		52	0	(416)
Executive Severance
Restructuring Cost and Reserve [Line Items]
Costs incurred		(711)	(930)	0
Executive Severance | Trucking
Restructuring Cost and Reserve [Line Items]
Costs incurred		(484)	(665)	0
Executive Severance | USAT Logistics
Restructuring Cost and Reserve [Line Items]
Costs incurred		$ (227)	$ (265)	$ 0