Income taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Income taxes | ||
| Unrecognized tax benefits | $ 0 | $ 0 |
| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of unrecognized tax benefits. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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