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Stock-Based Compensation - Schedule of stock option activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Shares arising out of options
Outstanding, shares arising out of options, beginning balance	7,347,241
Granted, shares arising out of options (in shares)	1,831,180	431,924
Forfeited, shares arising out of options	(25,000)
Expired, shares arising out of options	0
Exercised, shares arising out of options	(1,020,125)
Outstanding, shares arising out of options, ending balance	8,133,296		7,347,241
Vested and expected to vest thereafter, shares arising out of options	7,485,096
Vested and exercisable, shares arising out of options	3,242,333
Weighted average grant-date fair value of options granted during the period	$ 11.35
Weighted average exercise price
Outstanding weighted average exercise price, beginning balance (in usd per share)	26.41
Granted, weighted average exercise price (in usd per share)	43.98
Forfeited, weighted average exercise price (in usd per share)	31.50
Expired, weighted average exercise price (in usd per share)	0
Exercised, weighted average exercise price (in usd per share)	20.50
Outstanding weighted average exercise price, ending balance (in usd per share)	31.10		$ 26.41
Vested and expected to vest thereafter, weighted average exercise price (in usd per share)	30.24
Vested and exercisable, weighted average exercise price (in usd per share)	$ 23.94
Weighted average remaining contractual life (years)
Outstanding weighted average remaining contractual life (years)	6 years 3 months 18 days		5 years 8 months 12 days
Vested and expected to vest thereafter, weighted average remaining contractual life (years)	6 years 3 months 18 days
Vested and exercisable, weighted average remaining contractual life (years)	3 years 8 months 12 days
Aggregate intrinsic value
Outstanding aggregate intrinsic value	$ 134,565		$ 0
Exercised, aggregate intrinsic value	26,085
Vested and expected to vest thereafter, aggregate intrinsic value	130,045
Vested and exercisable, aggregate intrinsic value	$ 76,436

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract]

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Term [Abstract]

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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