Stockholder's Equity (Deficit) - Summary of Assumptions Used to Value Convertible Preferred Stock Warrants (Details) - Convertible Preferred Stock Warrants	Dec. 31, 2017	Dec. 31, 2016
Minimum | Expected term (in years)
Class Of Warrant Or Right [Line Items]
Fair value assumptions term	3 years	3 years 2 months 12 days
Minimum | Risk-free interest rate
Class Of Warrant Or Right [Line Items]
Fair value assumptions	1.5	0.7
Minimum | Expected volatility
Class Of Warrant Or Right [Line Items]
Fair value assumptions	44	46
Maximum | Expected term (in years)
Class Of Warrant Or Right [Line Items]
Fair value assumptions term	9 years 8 months 12 days	3 years 10 months 24 days
Maximum | Risk-free interest rate
Class Of Warrant Or Right [Line Items]
Fair value assumptions	2.3	1.6
Maximum | Expected volatility
Class Of Warrant Or Right [Line Items]
Fair value assumptions	51	48