Revenue - Disaggregation of Revenue by Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 132,583	$ 114,235	$ 392,977	$ 323,263
Freight
Disaggregation of Revenue [Line Items]
Revenues	113,520	99,881	338,351	282,240
Fuel Surcharge
Disaggregation of Revenue [Line Items]
Revenues	15,982	11,849	46,990	35,011
Accessorial
Disaggregation of Revenue [Line Items]
Revenues	3,081	2,505	7,636	6,012
Trucking
Disaggregation of Revenue [Line Items]
Revenues	85,529	76,450	249,831	218,275
Trucking | Freight
Disaggregation of Revenue [Line Items]
Revenues	71,774	65,869	211,503	187,384
Trucking | Fuel Surcharge
Disaggregation of Revenue [Line Items]
Revenues	11,880	9,540	35,178	27,555
Trucking | Accessorial
Disaggregation of Revenue [Line Items]
Revenues	1,875	1,041	3,150	3,336
USAT Logistics
Disaggregation of Revenue [Line Items]
Revenues	47,054	37,785	143,146	104,988
USAT Logistics | Freight
Disaggregation of Revenue [Line Items]
Revenues	41,746	34,012	126,848	94,856
USAT Logistics | Fuel Surcharge
Disaggregation of Revenue [Line Items]
Revenues	4,102	2,309	11,812	7,456
USAT Logistics | Accessorial
Disaggregation of Revenue [Line Items]
Revenues	$ 1,206	$ 1,464	$ 4,486	$ 2,676