Investments in and Advances to Equity Accounted Investments - Schedule of Investments in and Advances to Equity Accounted Investments (Details) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Schedule of Equity Method Investments [Line Items] | ||
| Investment in and advances to equity accounted investments | $ 24,811 | $ 25,460 |
| High-Q Joint Venture | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Investment in and advances to equity accounted investments | 24,811 | 24,546 |
| Gemini Tankers L.L.C. | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Investment in and advances to equity accounted investments | $ 0 | $ 914 |