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Dividends - Summary of Dividends (Parenthetical) (Detail) - R / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
 [1]
Dec. 31, 2015
 [1]
Dec. 31, 2014
Final Dividend [Member]        
Disclosure of Dividends [Line Items]        
Dividends declared per share   R 0.60 R 0.21 R 0.20
Dividend declared date Feb. 16, 2017      
Interim Dividend [Member]        
Disclosure of Dividends [Line Items]        
Dividends declared per share R 0.40 R 0.50 R 0.04  
Approved dividend [member]        
Disclosure of Dividends [Line Items]        
Final dividend approved by the Board, Value R 0.5      
[1] As Restated - Refer note 40 for further details.