Estimated Fair Value of Certain Stock-Based Awards Using Black-Scholes-Merton Valuation Model (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)	5 years 1 month 13 days	6 years 3 months 18 days	5 years 1 month 13 days	6 years 4 months 2 days
Weighted-average volatility	69.00%	75.00%	70.00%	75.00%
Risk-free interest rate	1.73%
Risk-free interest rate Minimum		1.12%	1.73%	1.08%
Risk-free interest rate Maximum		1.14%	1.75%	1.14%
Expected dividends
Stock Appreciation Units (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)	2 years 4 months 24 days	2 years 3 months 29 days	2 years 3 months 7 days	2 years 5 months 19 days
Weighted-average volatility	56.00%	57.00%	57.00%	60.00%
Risk-free interest rate
Risk-free interest rate Minimum	0.13%	0.19%	0.13%	0.19%
Risk-free interest rate Maximum	0.90%	0.30%	0.90%	0.46%
Expected dividends
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)	4 months 24 days	8 months 23 days	8 months 9 days	8 months 23 days
Weighted-average volatility	56.00%	48.00%	54.00%	48.00%
Risk-free interest rate	0.05%
Risk-free interest rate Minimum		0.09%	0.05%	0.09%
Risk-free interest rate Maximum		0.16%	0.13%	0.16%
Expected dividends