Leases (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Chartered-in vessels | |||
| Property Subject To Or Available For Operating Lease [Line Items] | |||
| Charter hire expense | $ 142,968 | $ 122,668 | $ 84,114 |
| Rent expense for office space | 2,876 | 2,648 | 2,748 |
| Logistics business | |||
| Property Subject To Or Available For Operating Lease [Line Items] | |||
| Charter hire expense | $ 114 | $ 1,564 | $ 1,521 |