Common Stock - Common Stock Reserved For Future Issuances (Details) - shares	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	66,539,405	67,675,796
Warrants, outstanding	40,538	313,741
Conversion of outstanding convertible preferred stock
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	58,264,577	58,264,577
Shares available for future stock option grants
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	509,584	1,698,790
Exercise and conversion of preferred stock warrants
Class of Stock [Line Items]
Common stock, shares reserved for future issuance		7,636
Stock option
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	7,717,070	7,391,052