Stockholders' Equity - Fair Value of Share-Based Payments was Estimated on Date of Grant Using Black-Scholes Option Pricing Model Based on Weighted Average Assumptions (Detail) |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
ESPP [Member] | |||
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items] | |||
Risk-free interest rate | 0.50% | 0.30% | 0.20% |
Volatility | 74.00% | 75.30% | 86.00% |
Expected term in years | 6 months | 6 months 22 days | 1 year 3 months |
Expected dividend yield | 0.00% | 0.00% | 0.00% |
Options [Member] | |||
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items] | |||
Risk-free interest rate | 1.90% | 1.70% | 1.90% |
Volatility | 74.00% | 79.40% | 77.10% |
Expected term in years | 6 years 5 months 9 days | 6 years 4 months 17 days | 6 years 3 months 18 days |
Expected dividend yield | 0.00% | 0.00% | 0.00% |