Summary of Significant Accounting Policies - Project Development Costs (Details) - USD ($) $ in Thousands |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Accounting Policies [Abstract] | ||
| Capitalized project development costs, noncurrent | $ 2,948 | $ 1,524 |
| X | ||||||||||
- Definition Capitalized Project Development Costs, Noncurrent No definition available.
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| X | ||||||||||
- References No definition available.
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