Description of Business and Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 534,060	$ 446,533	$ 429,099
Freight
Disaggregation of Revenue [Line Items]
Revenues	460,983	389,863	379,324
Fuel Surcharge
Disaggregation of Revenue [Line Items]
Revenues	63,805	48,216	40,929
Accessorial
Disaggregation of Revenue [Line Items]
Revenues	9,272	8,454	8,846
Trucking
Disaggregation of Revenue [Line Items]
Revenues	347,729	302,052	294,526
Trucking | Freight
Disaggregation of Revenue [Line Items]
Revenues	295,585	259,550	256,457
Trucking | Fuel Surcharge
Disaggregation of Revenue [Line Items]
Revenues	47,770	38,173	32,090
Trucking | Accessorial
Disaggregation of Revenue [Line Items]
Revenues	4,374	4,329	5,979
USAT Logistics
Disaggregation of Revenue [Line Items]
Revenues	186,331	144,481	134,573
USAT Logistics | Freight
Disaggregation of Revenue [Line Items]
Revenues	165,398	130,313	122,867
USAT Logistics | Fuel Surcharge
Disaggregation of Revenue [Line Items]
Revenues	16,035	10,043	8,839
USAT Logistics | Accessorial
Disaggregation of Revenue [Line Items]
Revenues	$ 4,898	$ 4,125	$ 2,867