Convertible Preferred Stock, Stockholders’ Equity (Deficit) and Equity Incentive Plan - Additional Information (Details) - USD ($)		1 Months Ended		6 Months Ended	12 Months Ended
	Apr. 23, 2019	Apr. 30, 2019	Oct. 31, 2015	Jul. 31, 2019	Jan. 31, 2019	Dec. 31, 2011
Class of Stock [Line Items]
Convertible preferred stock, shares outstanding (in shares)				0
Conversion of convertible preferred stock to common stock upon initial public offering				$ 159,552,000
Undesignated preferred stock shares authorized (in shares)				200,000,000	0
Undesignated referred stock par value (in dollars per share)				$ 0.001	$ 0.001
Common stock, par value (in dollars per share)				$ 0.001	$ 0.001
Stock options outstanding (in shares)		35,064,465		22,046,188
Unrecognized stock-based compensation expenses related to outstanding unvested stock options				$ 94,300,000
Proceeds from unvested shares of common stock				1,800,000	$ 1,800,000
Common Stock
Class of Stock [Line Items]
Conversion of convertible preferred stock to common stock upon initial public offering				$ 153,000
RSUs
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period				3 years 10 months 24 days
Unrecognized stock-based compensation expenses				$ 33,900,000
Number of shares of common stock unvested and subject to repurchase (in shares)				370,860	0
Stock options
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period				3 years 3 months 18 days
Employee Stock Purchase Plan
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period				1 year 10 months 24 days
Unrecognized stock-based compensation expenses				$ 78,500,000
Payroll deductions to participate in plan		20.00%
Maximum number of shares per employee (in shares)		3,000
Consecutive offering period		27 months
Restricted Stock Awards | Common Stock
Class of Stock [Line Items]
Number of shares of common stock unvested and subject to repurchase (in shares)				180,408
Restricted Stock Awards | Board of directors, member
Class of Stock [Line Items]
Vesting period of awards			4 years
Shares issued of common stock (in shares)			1,202,720
Grant date fair value (in dollars per share)			$ 0.14
Shares issued of common stock, value			$ 200,000
Shares vested on the grant date			481,088
2011 Plan
Class of Stock [Line Items]
Vesting period of awards						4 years
Shares of common stock reserved for grants of awards (in shares)					71,240,000
Number of shares available for future issuance (in shares)				24,300,889
2019 Plan
Class of Stock [Line Items]
Percentage of shares reserved increase				5.00%
2019 Employee Stock Purchase Plan | Employee Stock Purchase Plan
Class of Stock [Line Items]
Annual increase in shares for available for future issuance by percentage of the outstanding ordinary shares on the first day of such fiscal year.		1.00%
Annual increase in Number of shares of common stock available for future issuance		7,500,000
Initial public offering
Class of Stock [Line Items]
Undesignated preferred stock shares authorized (in shares)	200,000,000
Undesignated referred stock par value (in dollars per share)	$ 0.001
Convertible Preferred Stock
Class of Stock [Line Items]
Convertible preferred stock, shares outstanding (in shares)	152,665,804
Convertible preferred stock, shares issued (in shares)				0
Undesignated preferred stock shares authorized (in shares)				0	158,104,540
Undesignated referred stock par value (in dollars per share)				$ 0.001	$ 0.001
Convertible Preferred Stock | Initial public offering
Class of Stock [Line Items]
Conversion of convertible preferred stock to common stock upon initial public offering	$ 159,600,000
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				2,000,000,000	320,000,000
Class A Common Stock | Employee Stock Purchase Plan
Class of Stock [Line Items]
Percentage of purchase price of common stock to fair market value of common stock on offering or purchase date		85.00%
ESPP excess rate purchase right, value		$ 25,000
Shares issued of common stock (in shares)				0
Class A Common Stock | 2019 Plan
Class of Stock [Line Items]
Number of shares available for future issuance (in shares)				58,300,889
Numbers of additional shares authorized under the plan (in shares)				34,000,000
Class A Common Stock | 2019 Employee Stock Purchase Plan | Employee Stock Purchase Plan
Class of Stock [Line Items]
Number of shares available for future issuance (in shares)		9,000,000
Class A Common Stock | Initial public offering
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				2,000,000,000
Common stock, par value (in dollars per share)				$ 0.001
Class B Common Stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				300,000,000	300,000,000
Number of common stock subject to repurchase (in shares)				663,826	1,261,230
Weighted average price per share (in dollars per share)		$ 1.41		$ 2.71
Class B Common Stock | 2011 Plan
Class of Stock [Line Items]
Stock options outstanding (in shares)					35,064,465
Number of shares available for future issuance (in shares)					1,848,100
Class B Common Stock | Initial public offering
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				300,000,000
Common stock, par value (in dollars per share)				$ 0.001