Stockholders' Equity - Schedule of Common Stock Reserved for Issuance (Details) - shares	Sep. 30, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	4,357,320	3,064,876
Options Issued and Outstanding
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	3,289,677	2,141,868
2015 Stock Option and Incentive Plan
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	587,696	720,921
2015 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	479,947	202,087