Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments			2
Revenues
Total Operating Revenue	$ 413,862	$ 449,758	$ 829,225	$ 875,466
Operating Income
Total Operating Income	8,787	20,018	21,425	34,872
Truckload Segment [Member]
Revenues
Total Operating Revenue	374,405	391,397	743,524	762,564
Operating Income
Total Operating Income	7,503	18,590	17,344	31,093
Brokerage Segment [Member]
Revenues
Total Operating Revenue	39,457	58,361	85,701	112,902
Operating Income
Total Operating Income	$ 1,284	$ 1,428	$ 4,081	$ 3,779