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Dividends Declared and Paid - Summary of Dividends Declared and Paid (Parenthetical) (Detail) - $ / shares
 12 Months Ended
Jul. 13, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of dividends declared and paid on ordinary capital [line items]        
Dividends on ordinary shares, per share $ 0.90 $ 2.21 $ 0.90 $ 0.85
Final dividend [member]        
Disclosure of dividends declared and paid on ordinary capital [line items]        
Dividends on ordinary shares, per share   0.73 $ 0.90  
Special dividend [member]        
Disclosure of dividends declared and paid on ordinary capital [line items]        
Dividends on ordinary shares, per share   $ 1.48