Stock-based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Each Employee and Non-employee Stock Award on Grant Date Using Black Scholes Option Pricing Model (Detail) - Employee and Nonemployee Stock Option [Member] |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Dividend | 0.00% | 0.00% | 0.00% |
Minimum [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Volatility | 79.00% | 84.00% | 85.00% |
Expected term (in years) | 5 years | 5 years 6 months | 6 years 3 months |
Risk-free interest rate | 1.45% | 1.73% | 1.07% |
Maximum [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Volatility | 88.00% | 95.00% | 93.00% |
Expected term (in years) | 9 years 10 months 24 days | 9 years 10 months 24 days | 10 years |
Risk-free interest rate | 2.33% | 2.15% | 3.01% |