Capital Stock - Risk-Free Rate Based on U S Treasury Yield Curve (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected volatility	34.94%	34.47%	35.02%
Expected dividend yields	0.82%	0.47%	0.60%
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Risk-free rate	0.78%	1.95%	2.31%