Weighted-Average Assumptions used to Estimate Fair Value of Options Granted using Black-Scholes Option-Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2011 Year	Dec. 31, 2010 Year	Dec. 31, 2009 Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	5.9	5.9	6.0
Risk-free interest rate	1.40%	2.30%	3.00%
Expected volatility	50.60%	50.80%	53.20%
Expected dividend yield