Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance Under Equity Incentive Plans (Detail)	Jun. 30, 2020 shares
Class Of Stock [Line Items]
Total reserved shares of common stock	16,335,544
2014 Equity Incentive Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	14,127,804
2018 Inducement Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	1,141,086
2014 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	1,066,654