Convertible Preferred Stock and Stockholders' Equity (Deficit) - Schedule of Reserved Common Stock on an if-Converted Basis for Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	8,310,754	5,259,271
Common Stock Options Issued and Outstanding
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	4,738,004	1,458,080
Remaining Shares Available for Issuance under 2015 & 2018 Stock Plan
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	2,315,099	3,801,191
Unvested Restricted Stock Issued as Part of Collaboration Agreement
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,257,651