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Contract liabilities and deferred income - Schedule of Contract liabilities and deferred income (Parenthetical) (Detail) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Contract Liabilities And Deferred Income [Line Items]    
Contract Liabilities $ 30,189,000 $ 26,911,000
Deferred revenue and income, non-current [1] 920,000 1,223,000
Membership subscription [Member]    
Contract Liabilities And Deferred Income [Line Items]    
Deferred revenue and income, non-current 751,000 781,000
Government grants [Member]    
Contract Liabilities And Deferred Income [Line Items]    
Deferred revenue and income, non-current $ 169,000 $ 442,000
[1] As of December 31, 2019 and 2020, the non-current portion consists of membership subscription of USD 781,000 and USD 751,000, and government grants of USD 442,000 and USD 169,000, respectively.