Convertible Preferred Stock, Stockholders’ Equity (Deficit) and Equity Incentive Plan - Additional Information (Details)	1 Months Ended		12 Months Ended
	Apr. 30, 2019 USD ($) vote shares	May 31, 2017 USD ($) $ / shares shares	Jan. 31, 2020 USD ($) $ / shares shares	Jan. 31, 2019 USD ($) $ / shares shares	Jan. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2011	Apr. 23, 2019 USD ($) $ / shares shares	Nov. 30, 2018 vote $ / shares shares	Jan. 31, 2017 USD ($) shares
Class of Stock [Line Items]
Convertible preferred stock, shares outstanding (in shares)			0	152,665,804	152,665,804				154,031,604
Conversion of convertible preferred stock to common stock upon initial public offering | $			$ 0	$ 159,552,000	$ 159,552,000				$ 159,757,000
Convertible preferred stock, shares issued (in shares)			0	152,665,804
Undesignated preferred stock shares authorized (in shares)			200,000,000	0
Undesignated referred stock par value (in dollars per share) | $ / shares			$ 0.001	$ 0.001
Temporary equity repurchased during period (in shares)					1,365,800
Repurchase of Series A convertible preferred stock | $					$ (205,000)
Common stock, conversion features, term			6 months
Initial offering period			15 years
Common stock, par value (in dollars per share) | $ / shares			$ 0.001	$ 0.001
Stock options outstanding (in shares)			16,833,009	35,064,465
Weighted average grant date fair value of options for employees (in dollars per share) | $ / shares			$ 25.17	$ 6.28	$ 0.67
Expected unrecognized stock-based compensation expenses related to outstanding unvested stock options | $			$ 76,600,000
Number of shares available for future issuance (in shares)			60,911,996	189,578,369
Number of purchase periods | vote	4
Proceeds for unvested shares of common stock | $			$ 1,200,000	$ 1,800,000
Stock-based compensation expense | $			73,109,000	$ 8,941,000	$ 10,329,000
RSUs
Class of Stock [Line Items]
Unrecognized stock-based compensation expenses | $			$ 142,800,000
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period			3 years 7 months 6 days
Number of shares available for future issuance (in shares)			1,964,668	0
Purchase rights committed under the ESPP
Class of Stock [Line Items]
Unrecognized stock-based compensation expenses | $			$ 55,700,000
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period			1 year 4 months 24 days
Number of shares available for future issuance (in shares)			1,323,662	0
Payroll deductions to participate in plan	20.00%
Maximum number of shares per employee (in shares)	3,000
Consecutive offering period	27 months
Stock options
Class of Stock [Line Items]
Unrecognized stock-based compensation excepted to be recognized over a weighted-average period			2 years 9 months 18 days
Number of shares available for future issuance (in shares)			16,833,009	35,064,465
2011 Plan
Class of Stock [Line Items]
Vesting period of awards						4 years
Term of 2019 stock plan						5 years
Number of shares authorized (in shares)				71,240,000
Stock plan rate						10.00%
2011 Plan | Maximum
Class of Stock [Line Items]
Term of 2019 stock plan						10 years
2019 Plan
Class of Stock [Line Items]
Shares reserved for issuance, percentage	5.00%
2019 Plan | Maximum
Class of Stock [Line Items]
Term of 2019 stock plan			10 years
2019 Employee Stock Purchase Plan | Purchase rights committed under the ESPP
Class of Stock [Line Items]
Number of shares available for future issuance (in shares)			7,186,070	0
Percent of outstanding stock, maximum	1.00%
Number of additional shares allowable under the plan (in shares)	7,500,000
Share-based Compensation Arrangement By Share-based Payment Award, Percentage Voting Power Excluded From Participating In Plan			5.00%
Initial public offering
Class of Stock [Line Items]
Convertible preferred stock, shares outstanding (in shares)							152,665,804
Conversion of convertible preferred stock to common stock upon initial public offering | $							$ 159,600,000
Undesignated preferred stock shares authorized (in shares)							200,000,000
Undesignated referred stock par value (in dollars per share) | $ / shares							$ 0.001
Third-Party Stock Transaction | Chief Executive Officer
Class of Stock [Line Items]
Shares issued, price per share (in dollars per share) | $ / shares		$ 3.74
Stock-based compensation expense | $		$ 8,600,000
Shares issued (in shares)		2,899,136
Series A Preferred Stock
Class of Stock [Line Items]
Convertible preferred stock, shares outstanding (in shares)				61,717,700
Convertible preferred stock, shares issued (in shares)				61,717,700
Temporary equity repurchased during period (in shares)					1,365,800
Repurchase of Series A convertible preferred stock | $					$ 4,600,000
Class A Common Stock
Class of Stock [Line Items]
Common stock number of votes per share | vote								1
Common stock, shares issued (in shares)			123,391,114	0
Common stock, shares authorized (in shares)			2,000,000,000	320,000,000				320,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.001					$ 0.001
Class A Common Stock | Purchase rights committed under the ESPP
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)			490,268
Class A Common Stock | 2011 Plan
Class of Stock [Line Items]
Other shares authorized (in shares)	24,300,889
Class A Common Stock | 2019 Plan
Class of Stock [Line Items]
Number of shares authorized (in shares)	58,300,889
Number of additional shares authorized under the plan (in shares)	34,000,000
Class A Common Stock | 2019 Employee Stock Purchase Plan | Purchase rights committed under the ESPP
Class of Stock [Line Items]
Number of shares available for future issuance (in shares)	9,000,000
Class B Common Stock
Class of Stock [Line Items]
Common stock number of votes per share | vote								10
Common stock, shares issued (in shares)			155,336,747
Common stock, shares authorized (in shares)			300,000,000	300,000,000				300,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.001					$ 0.001
Number of common stock subject to repurchase (in shares)			466,819	1,261,230
Common stock subject to repurchase or cancellation (in dollars per share) | $ / shares			$ 2.58
Weighted average price per share (in dollars per share) | $ / shares			$ 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 grant (in shares)				1,848,100