Stock-Based Compensation - Black-Scholes Option-Pricing Model Assumptions Used To Calculate Fair Value of Employee Stock Options ESPP Purchases (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average risk-free interest rate	0.90%	1.60%	1.80%
Dividend yield	0.00%	0.00%	0.00%
Volatility factor	62.20%	63.80%	62.70%
Weighted average expected life	5 years	4 years 10 months 24 days	4 years 10 months 24 days
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average risk-free interest rate	0.10%	0.10%	0.20%
Dividend yield	0.00%	0.00%	0.00%
Volatility factor	45.60%	53.60%	47.80%
Weighted average expected life	6 months	6 months	6 months