Net Loss Per Share - Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	16,168,362	12,815,477
Options issued and outstanding and ESPP shares issuable
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	14,530,378	12,202,568
Restricted shares subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	1,637,984	524,359
Early exercised common stock subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	0	88,550