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Fair value measurements - Schedule of financial instruments measured at fair value (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]    
Fair value measurements, Short term investments $ 117,821 $ 102,847
Fair value measurements, Total 48,993 292
Investments in financial instruments [Member]    
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]    
Fair value measurements, Short term investments 48,993 292
Significant other observable inputs (Level 2) [Member]    
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]    
Fair value measurements, Total 48,993 292
Significant other observable inputs (Level 2) [Member] | Investments in financial instruments [Member]    
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]    
Fair value measurements, Short term investments $ 48,993 $ 292