Net Loss per Share - Summary of Antidilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share (in shares)	20,428	14,592
Stock options and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share (in shares)	20,016	14,477
Shares issuable under the ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share (in shares)	297	0
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share (in shares)	115	115