Convertible Preferred Stock, Stockholders’ Equity (Deficit) and Equity Incentive Plan - Additional Information (Details) - USD ($)			1 Months Ended		9 Months Ended	12 Months Ended
	Oct. 31, 2019	Apr. 23, 2019	Apr. 30, 2019	Oct. 31, 2015	Oct. 31, 2019	Jan. 31, 2019	Dec. 31, 2011	Jul. 31, 2019	Jan. 31, 2016
Class of Stock [Line Items]
Convertible preferred stock, shares outstanding (in shares)	0				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				200,000,000	0
Undesignated referred stock par value (in dollars per share)	$ 0.001				$ 0.001	$ 0.001
Common stock, par value (in dollars per share)	$ 0.001				$ 0.001	$ 0.001
Stock options outstanding (in shares)	19,226,825				19,226,825			35,064,465
Unrecognized stock-based compensation expenses related to outstanding unvested stock options	$ 86,600,000				$ 86,600,000
Proceeds from unvested shares of common stock					1,400,000	$ 1,800,000
RSUs
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period	3 years 9 months 18 days
Unrecognized stock-based compensation expenses	$ 130,900,000				130,900,000
Employee Stock Purchase Plan
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period	1 year 7 months 6 days
Unrecognized stock-based compensation expenses	$ 62,400,000				$ 62,400,000
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 | Board of directors
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 (in shares)				481,088
Stock options
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period	3 years
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				24,300,889
2019 Plan
Class of Stock [Line Items]
Percentage of shares reserved increase	5.00%				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				0
Undesignated preferred stock shares authorized (in shares)	0				0	158,104,540
Undesignated referred stock par value (in dollars per share)	$ 0.001				$ 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				2,000,000,000	320,000,000
Issuance of common stock reserved for charitable donation (in shares)					500,000
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				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				2,000,000,000
Common stock, par value (in dollars per share)	$ 0.001				$ 0.001
Class B Common Stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	300,000,000				300,000,000	300,000,000
Number of common stock subject to repurchase (in shares)					527,848	1,261,230
Weighted average price per share (in dollars per share)	$ 2.60				$ 2.60			$ 1.41
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				300,000,000
Common stock, par value (in dollars per share)	$ 0.001				$ 0.001