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Assumptions used to Value Options (Detail) (ZAR)
6 Months Ended 12 Months Ended
Dec. 31, 2010
Dec. 31, 2011
Jun. 30, 2010
Stock Appreciation Rights
     
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Weighted average exercise price - Rand 93.89 119.17 90.84
Weighted average expected volatility (based on a statistical analysis of the share price on a weighted moving average basis for the expected term of the option) 50.20% 46.40% 52.00%
Expected term   5 years 10 months 24 days  
Historical dividend yield 1.00% 1.70% 1.00%
Weighted average risk free interest rate 6.90% 6.90% 7.90%
Weighted average fair value - Rand 55.06 51.66 43.82
Stock Appreciation Rights | Minimum
     
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Expected term 3 years   3 years
Stock Appreciation Rights | Maximum
     
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Expected term 4 years 2 months 12 days   4 years 2 months 12 days
Restricted Stock
     
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Weighted average expected volatility (based on a statistical analysis of the share price on a weighted moving average basis for the expected term of the option) 50.10% 64.10% 50.40%
Expected term 3 years 3 years 3 years
Historical dividend yield 1.90% 1.70% 1.40%
Weighted average risk free interest rate 0.20% 0.20% 0.20%
Weighted average fair value - Rand 191.38 206.27 155.78