| Summary of Segment Information | 
 Segment results from operations for the three months ended March 31, 2021 and 2020 are as follows:   
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|   | 
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Three Months Ended March 31, 2021 | 
 
|   | 
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Expedited Freight | 
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Intermodal | 
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Eliminations & Other | 
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Consolidated | 
 
| External revenues | 
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$ | 
303,531  | 
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$ | 
58,502  | 
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$ | 
—  | 
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$ | 
362,033  | 
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| Intersegment revenues | 
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655  | 
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12  | 
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(498) | 
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169  | 
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| Depreciation | 
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4,993  | 
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799  | 
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3  | 
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5,795  | 
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| Amortization | 
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1,805  | 
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1,637  | 
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—  | 
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3,442  | 
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| Income (loss) from continuing operations | 
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24,530  | 
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4,509  | 
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(6,315) | 
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22,724  | 
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| Purchases of property and equipment | 
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2,411  | 
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284  | 
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—  | 
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2,695  | 
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|   | 
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Three Months Ended March 31, 2020 | 
 
|   | 
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Expedited Freight | 
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Intermodal | 
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Eliminations & Other | 
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Consolidated | 
 
| External revenues | 
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$ | 
253,140  | 
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$ | 
52,455  | 
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$ | 
—  | 
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$ | 
305,595  | 
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| Intersegment revenues | 
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485  | 
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5  | 
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(528) | 
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(38) | 
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| Depreciation | 
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4,908  | 
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1,053  | 
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18  | 
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5,979  | 
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| Amortization | 
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1,787  | 
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1,568  | 
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—  | 
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3,355  | 
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| Income (loss) from continuing operations | 
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15,179  | 
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3,713  | 
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(3,120) | 
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15,772  | 
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| Purchases of property and equipment | 
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2,405  | 
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246  | 
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—  | 
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2,651  | 
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| Total Assets | 
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| As of March 31, 2021 | 
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$ | 
934,602  | 
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$ | 
204,178  | 
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$ | 
(122,879) | 
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$ | 
1,015,901  | 
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| As of December 31, 2020 | 
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905,081  | 
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221,963  | 
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(153,750) | 
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973,294  | 
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Revenue from the individual services within the Expedited Freight segment for the three months ended March 31, 2021 and 2020 are as follows: 
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Three Months Ended | 
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March 31, 2021 | 
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March 31, 2020 | 
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| Expedited Freight revenue: | 
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| Network | 
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$ | 
178,627  | 
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$ | 
152,009  | 
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| Truckload | 
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52,380  | 
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47,529  | 
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| Final Mile | 
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62,256  | 
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47,802  | 
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| Other | 
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10,923  | 
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6,285  | 
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| Total | 
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$ | 
304,186  | 
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$ | 
253,625  | 
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