Stock-based Compensation - Additional Information (Detail)	3 Months Ended	9 Months Ended
Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) Installment $ / shares shares
2021 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of purchase price for each share of common stock purchased of lower of fair market value per share on first day of applicable offering period		85.00%
Maximum offering period		27 months
Initial offering period beginning date		Jul. 15, 2021
Offering period expiration date		Jan. 14, 2022
Amount of eligible compensation for employee payroll deductions		$ 25,000
Monthly participant contributions limited to prevent prejudicial advantages to higher compensated employees		$ 1,000
Purchases related to ESPP \| shares	0	0
Stock-based compensation expense	$ 500,000	$ 500,000
2021 Employee Stock Purchase Plan [Member] \| The Timing of Payroll Deductions [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Amount withheld on behalf of employees for a future purchase		$ 2,100,000
2021 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of eligible compensation for employee payroll deductions	15.00%	15.00%
Class A Common Stock [Member] \| 2021 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance \| shares	3,200,000	3,200,000
2017 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of options exercised		$ 600,000
2017 Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value of RSUs \| $ / shares	$ 62.92	$ 62.92
Number of vesting equal annual installments \| Installment		4
Compensation cost related to nonvested awards not yet recognized	$ 37,200,000	$ 37,200,000
Weighted average period of recognition		2 years 4 months 24 days
2017 Plan [Member] \| Class A Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance \| shares	14,622,416	14,622,416

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Discount rate from fair value on offering date that participants pay for shares.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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