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Stock-Based Compensation - Additional Information (Detail) - USD ($) | 12 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Number of options outstanding | 4,539,403 | 4,773,670 |
RSU awards vesting, description | At vesting, each outstanding RSU will be exchanged for one share of the Company’s Common Stock. RSU recipients may elect to net share settle upon vesting, in which case the Company pays the employee’s income taxes due upon vesting and withholds a number of shares of Common Stock of equal value. RSU awards generally vest subject to the satisfaction of service requirements or the satisfaction of both service requirements and achievement of certain performance targets. |  |
Employee Stock Option |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Stock-based compensation expense | $ 9,719,116 | $ 3,955,216 | $ 3,265,348
Grant date fair value of the options granted | 34,582,743 | 12,137,250 | 4,141,318
Intrinsic value of options exercised | 44,082,294 | 24,561,189 | 5,805,317
Unrecognized pre-tax compensation expense | $ 36,355,846 |  |
Weighted average period to recognize pre-tax compensation expense | 3 years 1 month 6 days |  |
Dividend yield | 0.00% |  |
Restricted Stock Units (RSUs) |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Stock-based compensation expense | $ 33,663,871 | $ 8,438,107 | $ 5,189,259
Weighted average period to recognize pre-tax compensation expense | 3 years 1 month 6 days |  |
Number of restricted stock units outstanding, granted | 2,687,096 |  |
Unrecognized pre-tax compensation expense | $ 88,548,649 |  |
Additional unrecognized pre-tax compensation expense | $ 38,000,000.0 |  |
2004 Equity Incentive Plan |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Shares reserve for issuance | 673,262 |  |
2004 Equity Incentive Plan | Employee Stock Option |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Number of options outstanding | 673,262 |  |
2013 Incentive Plan |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Shares reserve for issuance | 5,598,345 |  |
2013 Incentive Plan | Employee Stock Option |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Number of options outstanding | 2,611,625 |  |
2013 Incentive Plan | Restricted Stock Units (RSUs) |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Number of restricted stock units outstanding | 2,588,000 |  |
Number of restricted stock units outstanding, granted | 1,754,071 |  |
Outside Of Equity Compensation Plans |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Shares reserve for issuance | 1,254,516 |  |
Outside Of Equity Compensation Plans | Restricted Stock Units (RSUs) |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Shares reserve for issuance | 936,025 |  |
Number of restricted stock units outstanding, granted | 933,025 |  |

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