Net Loss Per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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)	20,236,000	76,971,000	63,500,000
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	58,615,000	45,960,000
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)	14,020,000	17,571,000	15,628,000
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)	736,000	0	1,127,000
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)	695,000	785,000	785,000
Restricted Stock Units (RSUs)
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)	4,708,000	0	0
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)	77,000	0	0
Performance-Based RSUs
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)		1,826,667