Basis of Presentation and Significant Accounting Policies - Fair Value Assumptions (Details) |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|
| Stock-based Compensation, Valuation Assumptions | ||||
| Risk-free interest rate | 2.84% | 1.95% | ||
| Risk-free interest rate (minimum) | 2.49% | 1.95% | ||
| Risk-free interest rate (maximum) | 2.84% | 2.07% | ||
| Expected dividend yield | 0.00% | 0.00% | 0.00% | 0.00% |
| Expected volatility | 56.10% | 57.90% | ||
| Expected volatility (minimum) | 54.60% | 59.80% | ||
| Expected volatility (maximum) | 56.10% | 61.00% | ||
| Minimum | ||||
| Stock-based Compensation, Valuation Assumptions | ||||
| Expected term (years) | 6 years 2 months 16 days | 6 years 2 months 22 days | 6 years 2 months 5 days | 6 years 29 days |
| Maximum | ||||
| Stock-based Compensation, Valuation Assumptions | ||||
| Expected term (years) | 6 years 8 months 9 days | 6 years 6 months 18 days | 6 years 8 months 9 days | 6 years 7 months 13 days |