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Capital stock - Movement of Ordinary Shares Issued (Detail) - Ordinary shares [member] - shares
shares in Thousands
 12 Months Ended
Aug. 15, 2018
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of classes of share capital [line items]        
Beginning balance   727,240 727,265 856,059
Restricted shares – cancelled   (25) (349)
Restricted shares – uncancelled       (23)
Capital reduction 132,945     (128,422)
Ending balance   727,240 727,240 727,265