| Property, plant and equipment, net - Depreciation Expense (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | |
| Property, plant and equipment, net | ||||
| Depreciation expense | $ 1,395 | $ 779 | $ 3,418 | $ 2,290 | 
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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- References No definition available. 
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