Estimated Fair Value of Certain Stock-Based Awards Using Black-Scholes-Merton Valuation Model (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Employee Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)	5 years 9 months 11 days	6 years 6 months 18 days	5 years 6 months 7 days	6 years 5 months 23 days
Weighted-average volatility	66.00%	71.00%	68.00%	72.00%
Risk-free interest rate		1.82%
Risk-free interest rate Minimum	1.62%		1.62%	1.08%
Risk-free interest rate Maximum	1.88%		1.88%	1.82%
Expected dividends	0.00%	0.00%	0.00%	0.00%
Stock Appreciation Units (SARs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)	2 years 5 months 19 days	1 year 11 months 1 day	2 years 5 months 16 days	2 years 3 months 15 days
Weighted-average volatility	54.00%	52.00%	56.00%	57.00%
Risk-free interest rate Minimum	0.47%	0.15%	0.13%	0.14%
Risk-free interest rate Maximum	0.88%	0.66%	0.90%	0.66%
Expected dividends	0.00%	0.00%	0.00%	0.00%
ESPP Purchase Rights [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)		8 months 23 days	8 months 9 days	8 months 23 days
Weighted-average volatility		48.00%	54.00%	48.00%
Risk-free interest rate	0.00%
Risk-free interest rate Minimum		0.09%	0.05%	0.09%
Risk-free interest rate Maximum		0.16%	0.13%	0.16%
Expected dividends	0.00%	0.00%	0.00%	0.00%