Net Loss Per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (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]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	18,738	78,121
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	0	58,615
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	12,629	16,757
Restricted stock awards subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	614	982
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	695	785
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	4,713	982
ESPP obligations
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential outstanding shares of common stock excluded from computation of diluted net loss per share attributable to common stockholders (in shares)	87	0