REVENUE RECOGNITION - Disaggregation of Revenue by Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Disaggregation of Revenue
Revenues	$ 170,031	$ 123,737	$ 328,536	$ 250,510
Contract assets	2,200		2,200		$ 1,100
Operating Segments
Disaggregation of Revenue
Revenues			328,536	250,510
Intersegment Eliminations
Disaggregation of Revenue
Revenues	(14,079)	(3,628)	(27,058)	(6,674)
Trucking
Disaggregation of Revenue
Revenues	105,102	87,920	207,878	180,921
Trucking | Operating Segments
Disaggregation of Revenue
Revenues	105,361	88,627	208,464	182,622
Trucking | Intersegment Eliminations
Disaggregation of Revenue
Revenues	(259)	(707)	(586)	(1,701)
USAT Logistics
Disaggregation of Revenue
Revenues	64,929	35,817	120,658	69,589
USAT Logistics | Operating Segments
Disaggregation of Revenue
Revenues	78,749	38,738	147,130	74,562
USAT Logistics | Intersegment Eliminations
Disaggregation of Revenue
Revenues	(13,820)	(2,921)	(26,472)	(4,973)
Freight
Disaggregation of Revenue
Revenues	149,371	110,093
Freight | Operating Segments
Disaggregation of Revenue
Revenues			290,244	219,970
Freight | Intersegment Eliminations
Disaggregation of Revenue
Revenues	(13,545)	(3,461)	(26,149)	(6,154)
Freight | Trucking | Operating Segments
Disaggregation of Revenue
Revenues	90,712	78,514	181,727	159,417
Freight | USAT Logistics | Operating Segments
Disaggregation of Revenue
Revenues	72,204	35,040	134,666	66,707
Fuel Surcharge
Disaggregation of Revenue
Revenues	17,073	10,534
Fuel Surcharge | Operating Segments
Disaggregation of Revenue
Revenues			31,315	24,546
Fuel Surcharge | Intersegment Eliminations
Disaggregation of Revenue
Revenues	(534)	(167)	(909)	(520)
Fuel Surcharge | Trucking | Operating Segments
Disaggregation of Revenue
Revenues	12,038	8,083	22,358	19,371
Fuel Surcharge | USAT Logistics | Operating Segments
Disaggregation of Revenue
Revenues	5,569	2,618	9,866	5,695
Accessorial
Disaggregation of Revenue
Revenues	3,587	3,110
Accessorial | Operating Segments
Disaggregation of Revenue
Revenues			6,977	5,994
Accessorial | Trucking | Operating Segments
Disaggregation of Revenue
Revenues	2,611	2,030	4,379	3,834
Accessorial | USAT Logistics | Operating Segments
Disaggregation of Revenue
Revenues	$ 976	$ 1,080	$ 2,598	$ 2,160