Prepaid Tires, Property, Equipment and Depreciation (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Amortization Period of Tires	2 years
Sold revenue equipment in other current assets	$ 5,600	$ 3,904	$ 900
Tractors [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment, Salvage Value	15
Trailers [Member]
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment, Salvage Value	$ 4