Stockholders' Equity - Assumptions (Details) |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected term | 6 years 6 months | ||
Minimum | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Risk-free interest rate (percent) | 2.00% | 1.30% | 1.70% |
Expected volatility (percent) | 43.00% | 48.00% | 50.00% |
Expected term | 6 years 6 months | 6 years 7 months 6 days | |
Maximum | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Risk-free interest rate (percent) | 2.20% | 1.90% | 2.00% |
Expected volatility (percent) | 47.00% | 50.00% | 58.00% |
Expected term | 6 years 9 months 18 days | 6 years 8 months 12 days |