Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | ||
| Impairment loss | $ (34) | |
| One vessel | ||
| Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | ||
| Impairment loss | $ 32,930 |