Revenue (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||||
|---|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Jan. 01, 2018 |
Dec. 31, 2017 |
|
| Disaggregation of Revenue [Line Items] | ||||||
| Retained earnings | $ 104,783 | $ 104,783 | $ 91,242 | |||
| Revenue | 634,811 | $ 470,086 | 1,211,902 | $ 885,838 | ||
| Truckload | ||||||
| Disaggregation of Revenue [Line Items] | ||||||
| Revenue | 443,711 | 314,668 | 844,186 | 595,011 | ||
| Less than truckload | ||||||
| Disaggregation of Revenue [Line Items] | ||||||
| Revenue | 160,584 | 129,927 | 307,818 | 243,788 | ||
| Other revenue | ||||||
| Disaggregation of Revenue [Line Items] | ||||||
| Revenue | 30,516 | 25,490 | 59,898 | 47,039 | ||
| Transactional | ||||||
| Disaggregation of Revenue [Line Items] | ||||||
| Revenue | 502,788 | 371,394 | 955,897 | 704,355 | ||
| Managed Transportation | ||||||
| Disaggregation of Revenue [Line Items] | ||||||
| Revenue | $ 132,023 | $ 98,692 | 256,005 | $ 181,483 | ||
| Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | ||||||
| Disaggregation of Revenue [Line Items] | ||||||
| Retained earnings | $ 1,100 | |||||
| Revenues | $ 3,300 | |||||