Stock-Based Compensation - Schedule of Share-based Payment Award, Stock Options, Weighted-Average Valuation Assumptions (Detail) - Employee Stock Option [Member] |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||||
| Volatility | 71.80% | 61.70% | 73.50% | 58.80% |
| Weighted average risk-free interest rate | 1.30% | 1.60% | 1.40% | 1.70% |
| Expected dividend yield | 0.00% | 0.00% | 0.00% | 0.00% |
| Expected life of options (in years) | 6 years 1 month 6 days | 6 years | 5 years 9 months 18 days | 6 years |