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Short-term investments (Details) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]    
Investments, allowance for credit losses $ 0 $ 0
Maturities of Time Deposits, Description time deposits with original maturities between three months and one year  
Minimum    
Schedule Of Available For Sale Securities [Line Items]    
Time deposits, Maturity period 3 months  
Maximum    
Schedule Of Available For Sale Securities [Line Items]    
Time deposits, Maturity period 1 year