Summary of Significant Accounting Policies - Energy Assets (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
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| Accounting Policies [Abstract] | |||||
| Interest costs capitalized | $ 744 | $ 1,369 | $ 1,738 | $ 2,527 | |
| Minimum qualifying operating period for prorated repayments of grants | 5 years | ||||
| Deferred grant income | $ 6,912 | $ 6,912 | $ 7,188 | ||
| X | ||||||||||
- Definition Government Grant, Qualification Requirement, Prorated Repayment Effective Period from Date Placed in Service No definition available.
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of interest capitalized during the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of unearned revenue or income classified as other, expected to be taken into income after one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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