Prepaid Tires, Property, Equipment and Depreciation	6 Months Ended
	Jun. 30, 2021
Property, Plant and Depreciation [Abstract]
Property, Equipment, and Depreciation	Prepaid Tires, Property, Equipment, and DepreciationProperty and equipment are reported at cost, net of accumulated depreciation. Maintenance and repairs are charged to operations as incurred. New tires are capitalized separately from revenue equipment and are reported separately as “Prepaid tires” in the consolidated balance sheets and amortized over two years. Depreciation for financial statement purposes is computed by the straight-line method for all assets other than tractors. We recognize depreciation expense on new tractors (excludes assets acquired in an acquisition) using the 125% declining balance method. Revenue equipment acquired through acquisitions is generally revalued to current market values as of the acquisition date. These acquired assets are depreciated on a straight-line basis aligned with the remaining period of expected use. As acquired equipment is replaced, our fleet returns to our base methods of declining balance depreciation for tractors and straight-line depreciation for trailers. New tractors are depreciated to salvage values of $15,000 while new trailers are depreciated to salvage values of $4,000. At June 30, 2021, there was $1.5 million amounts receivable related to equipment sales recorded in other current assets compared to $3.4 million at December 31, 2020.