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Accounts receivable - Additional Information (Detail) - USD ($)
$ in Thousands
Jun. 30, 2021
Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Allowance for doubtful accounts receivable $ 29,031 $ 29,506
Unbilled revenue    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Accounts receivable balances $ 68,672 $ 91,538