Stockholders' Equity - Weighted Average Assumptions Used for the Fair Value of the Option Component of the Purchase Plan Shares Estimated at Grant Date Using Black-Scholes Option Pricing Model (Detail) (Employee Stock Purchase Plan, USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	1 year 2 months 12 days	1 year 6 months	1 year 3 months 18 days
Expected volatility	49.70%	43.20%	55.80%
Risk-free interest rate	0.20%	0.40%	0.40%
Expected dividends	0.00%	0.00%	0.00%
Weighted average fair value at grant date (usd per share)	$ 11.10	$ 7.29	$ 7.22