Prepaid Expenses and Other Current Assets (Table) (Details) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|---|
| PREPAID EXPENSES AND OTHER CURRENT ASSETS [Abstract] | |||
| Prepaid voyage and operating costs | $ 8,022 | $ 8,352 | |
| Claims receivable | 12,307 | 9,822 | |
| Prepaid other taxes | 4,520 | 4,279 | |
| Advances for working capital purposes | 18 | 4,486 | |
| Other | 2,516 | 1,957 | |
| Total prepaid expenses and other current assets | $ 34,697 | $ 27,383 | $ 28,896 |