Convertible Preferred Stock, Stockholders Equity (Deficit) and Equity Incentive Plan - Additional Information (Details) - USD ($)		1 Months Ended			3 Months Ended
	Apr. 23, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2015	Apr. 30, 2019	Apr. 30, 2018	Jan. 31, 2018
Class Of Stock [Line Items]
Temporary equity, shares issued		0	152,665,804		0
Convertible preferred stock outstanding		0	152,665,804		0
Undesignated preferred stock shares authorized		200,000,000	0		200,000,000
Undesignated referred stock par value		$ 0.001	$ 0.001		$ 0.001
Common stock, par value		$ 0.001	$ 0.001		$ 0.001
Stock options outstanding		22,624,060	35,064,465		22,624,060
Unrecognized stock-based compensation expenses related to outstanding unvested stock options		$ 93,600,000			$ 93,600,000
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period					3 years 4 months 24 days
Proceeds from unvested shares of common stock		$ 1,800,000	$ 1,800,000
Restricted Stock Awards | Common Stock
Class Of Stock [Line Items]
Number of shares of common stock unvested and subject to repurchase		180,408			180,408
Restricted Stock Awards | Board of Directors
Class Of Stock [Line Items]
Vesting period of awards				4 years
Shares issued of common stock				1,202,720
Grant date fair value				$ 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			71,240,000
2011 Plan | Maximum
Class Of Stock [Line Items]
Number of shares available for future issuance		24,300,889			24,300,889
2019 Plan
Class Of Stock [Line Items]
Percentage of shares reserved increase		5.00%			5.00%
Initial public offering
Class Of Stock [Line Items]
Conversion of convertible preferred stock to common stock upon initial public offering					$ 159,552,000
Undesignated preferred stock shares authorized		200,000,000			200,000,000
Undesignated referred stock par value		$ 0.001			$ 0.001
Initial public offering | Common Stock
Class Of Stock [Line Items]
Convertible securities converted to common stock, shares					152,665,804
Conversion of convertible preferred stock to common stock upon initial public offering					$ 153,000
Employee Stock Purchase Plan
Class Of Stock [Line Items]
Payroll deductions to participate in plan		20.00%			20.00%
Employee Stock Purchase Plan | 2019 Employee Stock Purchase Plan | Maximum
Class Of Stock [Line Items]
Annual increase in Number of shares of common stock available for future issuance		7,500,000
Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock outstanding			152,665,804			152,665,804	152,665,804
Convertible Preferred Stock | Initial public offering
Class Of Stock [Line Items]
Convertible securities converted to common stock, shares	152,665,804
Temporary equity conversion basis					one-to-one
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		2,000,000,000	320,000,000		2,000,000,000
Number of shares purchased under ESPP		0
ESPP excess rate purachse right, value		$ 25,000
Class A Common Stock | 2019 Plan
Class Of Stock [Line Items]
Numbers of additional shares authorized under the plan		34,000,000
Class A Common Stock | 2019 Plan | Maximum
Class Of Stock [Line Items]
Number of shares available for future issuance		58,300,889			58,300,889
Class A Common Stock | Initial public offering
Class Of Stock [Line Items]
Common stock, shares authorized		2,000,000,000			2,000,000,000
Common stock, par value		$ 0.001			$ 0.001
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 date		85.00%
Percentage of purchase price of common stock to fair market value of common stock on purchase date		85.00%
Class A Common Stock | Employee Stock Purchase Plan | 2019 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Number of shares available for future issuance		9,000,000			9,000,000
Class B Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized		300,000,000	300,000,000		300,000,000
Number of common stock subject to repurchase		697,564	1,261,230
Weighted average price per share		$ 2.59	$ 1.41		$ 2.59
Class B Common Stock | 2011 Plan
Class Of Stock [Line Items]
Stock options outstanding			35,064,465
Number of shares available for future issuance			1,848,100
Class B Common Stock | Initial public offering
Class Of Stock [Line Items]
Convertible securities converted to common stock, shares	152,665,804
Common stock, shares authorized		300,000,000			300,000,000
Common stock, par value		$ 0.001			$ 0.001
Class A and Class B Common Stock | Employee Stock Purchase Plan | 2019 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%