Segment Information (Details) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2017
USD ($)
|
Sep. 30, 2018
USD ($)
|
Dec. 31, 2016
USD ($)
|
|
| Segment Reporting Information [Line Items] | |||
| Number of Reportable Segments | 2 | ||
| Net book value of long-lived assets | $ 1,809,225 | $ 1,694,429 | $ 1,821,101 |
| Dry bulk vessels | |||
| Segment Reporting Information [Line Items] | |||
| Net book value of long-lived assets | 1,278,447 | 1,409,415 | |
| Logistics Business | |||
| Segment Reporting Information [Line Items] | |||
| Net book value of long-lived assets | $ 563,887 | $ 544,065 |