Weighted Average Assumptions of Fair Value Options Using Black-Scholes Option-Pricing Model (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%	0.00%
Risk-free interest rate, minimum	0.72%	2.90%	0.72%	2.90%
Risk-free interest rate, maximum	0.84%	3.50%	0.87%	3.70%
Expected life (in years)	5 years	5 years	5 years	5 years
Historical volatility, minimum	60.60%	60.70%	60.30%	60.70%
Historical volatility, maximum	60.70%	61.50%	60.80%	61.50%