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Summary of significant accounting policies (Details)
12 Months Ended
Dec. 31, 2019
Leasehold improvements [Member]  
Statement [Line Items]  
Property and equipment estimated useful life 5 years
Office equipment and furniture [Member]  
Statement [Line Items]  
Property and equipment estimated useful life 3 years
Vehicles [Member]  
Statement [Line Items]  
Property and equipment estimated useful life 5 years
Property [Member]  
Statement [Line Items]  
Property and equipment estimated useful life 20 years