Segment Reporting - Segment Reporting Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating revenue	$ 141,083	$ 132,583	$ 135,381	$ 125,013	$ 123,270	$ 114,235	$ 107,358	$ 101,670	$ 534,060	$ 446,533	$ 429,099
Operating loss	$ 8,713	$ 5,803	$ 4,311	$ 2,392	$ 5,493	$ 1,804	$ (2,966)	$ (6,399)	21,219	(2,068)	(7,516)
Depreciation and amortization									28,324	28,463	29,954
Trucking
Segment Reporting Information [Line Items]
Operating revenue									347,729	302,052	294,526
USAT Logistics
Segment Reporting Information [Line Items]
Operating revenue									186,331	144,481	134,573
Operating Segments | Trucking
Segment Reporting Information [Line Items]
Operating revenue									351,222	302,943	295,807
Operating loss									11,710	(9,667)	(14,789)
Depreciation and amortization									27,632	28,002	29,467
Operating Segments | USAT Logistics
Segment Reporting Information [Line Items]
Operating revenue									190,992	152,137	140,847
Operating loss									9,509	7,599	7,273
Depreciation and amortization									692	461	487
Intersegment Eliminations | Trucking
Segment Reporting Information [Line Items]
Operating revenue									(3,493)	(891)	(1,281)
Intersegment Eliminations | USAT Logistics
Segment Reporting Information [Line Items]
Operating revenue									(4,661)	(7,656)	(6,274)
Foreign Countries | Operating Segments | Trucking
Segment Reporting Information [Line Items]
Operating revenue									41,500	35,500	$ 36,900
Foreign Countries | Operating Segments | USAT Logistics
Segment Reporting Information [Line Items]
Operating revenue									$ 800	$ 2,100