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Stock-Based Compensation - Fair Value of Stock Options Granted and Compensation Expenses (Detail) (CAD)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 2.23%    2.26%
Expected dividend yield 2.00%    2.00%
Expected volatility 43.00%    35.00%
Expected time until exercise 4 years 6 months    4 years
Weighted average fair value of options granted or modified in year [Cdn$] 15.37    10.00