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Summary of significant accounting policies - Significant property and equipment (Details)
6 Months Ended
Jun. 30, 2022
Buildings  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 20 years
Machinery and equipment | Minimum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 5 years
Machinery and equipment | Maximum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 10 years
Transportation equipment | Minimum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 4 years
Transportation equipment | Maximum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 5 years
Office equipment | Minimum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 4 years
Office equipment | Maximum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 5 years
Electronic equipment | Minimum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 3 years
Electronic equipment | Maximum  
Estimated useful lives for significant property and equipment  
Plant and equipment useful life 5 years