Stockholders' Equity - Schedule of Common Stock Reserved for Issuance (Details) - shares	Mar. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	9,227,069	7,141,230
Options and Awards Issued and Outstanding
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	6,181,912	5,315,254
2015 Stock Option and Incentive Plan
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	1,440,826	685,435
2015 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares reserved for future issuance, shares	1,604,331	1,140,541