Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments									2
Revenues
Total Operating Revenue	$ 449,633	$ 428,503	$ 413,862	$ 415,363	$ 469,222	$ 460,227	$ 449,758	$ 425,708	$ 1,707,361	$ 1,804,915	$ 1,555,385
Operating Income
Total Operating Income (Loss)	$ 1,363	$ 3,282	$ 8,787	$ 12,638	$ 21,142	$ 22,892	$ 20,018	$ 14,854	26,070	78,906	28,608
Truckload Segment [Member]
Revenues
Total Operating Revenue									1,521,494	1,562,098	1,382,167
Operating Income
Total Operating Income (Loss)									24,071	69,088	25,200
Brokerage Segment [Member]
Revenues
Total Operating Revenue									185,867	242,817	173,218
Operating Income
Total Operating Income (Loss)									$ 1,999	$ 9,818	$ 3,408