Schedule of Weighted Average Valuation Assumptions (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.50%	1.30%	0.70%	1.90%
Dividend yield	0.40%	0.20%	0.30%	0.30%
Volatility factor	40.00%	45.00%	46.00%	44.00%
Expected life (in years)	3 years 6 months	3 years 9 months 18 days	4 years	4 years 3 months 18 days