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Dividends Declared and Paid - Summary of Dividends Declared and Paid (Parenthetical) (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of dividends declared and paid on ordinary capital [line items]      
Dividends on ordinary shares, per share $ 0.85 $ 0.85 $ 2.21
Final dividend [member]      
Disclosure of dividends declared and paid on ordinary capital [line items]      
Dividends on ordinary shares, per share $ 0.85 $ 0.85