Leases (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Construction of river and estuary tanker | |||
| Property Subject To Or Available For Operating Lease [Line Items] | |||
| Future minimum revenue | $ 41,380 | ||
| Lease term | 5 years | ||
| Logistics business | |||
| Property Subject To Or Available For Operating Lease [Line Items] | |||
| Charter hire expense | $ 1,564 | $ 1,521 | $ 1,307 |
| Future minimum revenue | 1,137,442 | ||
| Chartered-in vessels | |||
| Property Subject To Or Available For Operating Lease [Line Items] | |||
| Rent expense for office space | 2,648 | 2,748 | 2,508 |
| Charter hire expense | $ 122,668 | $ 84,114 | $ 134,364 |