Stock-Based Compensation - Summarize Information about Stock Options (Detail)	12 Months Ended
Sep. 30, 2020 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, beginning balance \| shares	4,773,670
Number of Options Outstanding, Granted \| shares	951,500
Number of Options Outstanding, Cancelled \| shares	(74,639)
Number of Options Outstanding, Exercised \| shares	(1,111,128)
Number of Options Outstanding, ending balance \| shares	4,539,403
Number of Options Outstanding, Exercisable \| shares	2,924,744
Weighted-Average Exercise Price Per Share, beginning balance \| $ / shares	$ 8.16
Weighted-Average Exercise Price Per Share, Granted \| $ / shares	48.19
Weighted-Average Exercise Price Per Share, Cancelled \| $ / shares	22.38
Weighted-Average Exercise Price Per Share, Exercised \| $ / shares	6.72
Weighted-Average Exercise Price Per Share, ending balance \| $ / shares	16.67
Weighted-Average Exercise Price Per Share, Exercisable \| $ / shares	$ 8.30
Weighted-Average Remaining Contractual Term	6 years 2 months 12 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 9 months 18 days
Aggregate Intrinsic Value \| $	$ 129,100,277
Aggregate Intrinsic Value, Exercisable \| $	$ 102,698,309

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

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

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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