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Prepayments and other current assets - Schedule of Prepayments and Other Assets (Parenthetical) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Receivable related to Linktoken disposal   $ 3,536
Employees [Member] | Minimum    
Term of interest-free loans to employees 5 years  
Employees [Member] | Maximum    
Term of interest-free loans to employees 10 years