Stock-Based Compensation - Schedule of Estimated Grant-date Fair Value of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions (Detail) |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2015 |
Jun. 30, 2014 |
Jun. 30, 2015 |
Jun. 30, 2014 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Expected term (in years) | 5 years 8 months 12 days | |||
| Expected volatility, Minimum | 75.00% | 75.00% | 81.00% | |
| Expected volatility, Maximum | 79.00% | 81.00% | 83.00% | |
| Expected volatility | 83.00% | |||
| Risk-free interest rate | 1.70% | 1.60% | ||
| Risk-free interest rate, Minimum | 1.50% | 1.50% | ||
| Risk-free interest rate, Maximum | 1.70% | 1.70% | ||
| Expected dividend rate | 0.00% | 0.00% | 0.00% | 0.00% |
| Minimum [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Expected term (in years) | 5 years 2 months 12 days | 6 years | 5 years | |
| Maximum [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Expected term (in years) | 10 years | 10 years | 5 years 8 months 12 days | |