Stock-Based Compensation - Narrative (Details)	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 target shares	May 31, 2021 USD ($) $ / shares shares	Oct. 31, 2021 USD ($) $ / shares shares	Oct. 31, 2020 USD ($) $ / shares	Oct. 31, 2021 USD ($) $ / shares shares	Oct. 31, 2020 USD ($) $ / shares	Jan. 31, 2021 USD ($) shares	Jan. 31, 2020 shares	Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) | shares			45,902,000		45,902,000		100,463,000
Aggregate intrinsic value, options vested | $			$ 3,100,000	$ 2,300,000	$ 7,500,000	$ 5,300,000
Intrinsic value of options exercised | $			$ 108,600,000	$ 1,700,000	$ 269,900,000	$ 4,600,000
Options granted (in USD per share) | $ / shares			$ 12.74	$ 3.13	$ 10.81	$ 3.05
Compensation expense not yet recognized | $			$ 88,900,000		$ 88,900,000		$ 26,800,000
Options granted (in shares) | shares					7,919,000			4,622,000
Stock-based compensation | $			$ 8,579,000	$ 2,056,000	$ 17,242,000	$ 5,678,000
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares) | shares			0		0
2021 Equity Incentive Plan | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) | shares	13,032,289
2021 ESPP | 2021 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rate	15.00%
Look-back period (in months)	27 months
2021 ESPP | 2021 Employee Stock Purchase Plan | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) | shares	3,271,090
Automatic annual increase period (in years)	10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition (in years)					1 year 6 months		1 year 3 months 18 days
Risk-free interest rate			0.89%	0.38%	1.10%	0.51%
Stock options | 2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period (in years)									10 years
Stock options | 2015 Equity Incentive Plan | Period one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage									25.00%
Award vesting period (in years)									1 year
Stock options | 2015 Equity Incentive Plan | Period two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)									36 months
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares) | shares					3,000,000			0
RSUs | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares) | shares		3,000,000
Grant date fair value | $		$ 8,800,000
Number of threshold stock price targets | target	8
Stock-based compensation | $			$ 800,000
Compensation expense not yet recognized | $		$ 8,800,000	$ 8,000,000		$ 8,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate		45.00%
Risk-free interest rate		1.52%
RSUs | Chief Executive Officer | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition (in years)		2 years 9 months 29 days
Threshold stock price target (in USD per share) | $ / shares		$ 95
RSUs | Chief Executive Officer | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition (in years)		7 years 6 months
Threshold stock price target (in USD per share) | $ / shares		$ 500