Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments			2
Revenues
Total Operating Revenue	$ 422,477	$ 413,862	$ 855,045	$ 829,225
Operating Income
Total Operating Income (Loss)	16,277	8,787	12,609	21,425
Truckload Segment [Member]
Revenues
Total Operating Revenue	376,448	374,405	758,540	743,524
Operating Income
Total Operating Income (Loss)	20,428	7,503	21,628	17,344
Brokerage Segment [Member]
Revenues
Total Operating Revenue	46,029	39,457	96,505	85,701
Operating Income
Total Operating Income (Loss)	$ (4,151)	$ 1,284	$ (9,019)	$ 4,081