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Stock-Based Compensation - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2020 | Mar. 31, 2019 | Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of options outstanding | 4,709,986 |  | 4,709,986 |  | 4,773,670
Number of options outstanding, granted |  |  | 653,500 |  |
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 | $ 2,527,839 | $ 1,017,065 | $ 4,136,910 | $ 1,807,500 |
Grant date fair value of the options granted | 17,968,884 | 7,580,360 | 26,599,374 | 8,137,249 |
Intrinsic value of options exercised | 8,605,235 | 6,806,594 | 30,245,825 | 8,122,294 |
Unrecognized pre-tax compensation expense | 34,707,355 |  | $ 34,707,355 |  |
Weighted average period to recognize pre-tax compensation expense |  |  | 3 years 6 months |  |
Dividend yield |  |  | 0.00% |  |
Restricted Stock Units (RSUs) |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of restricted stock units outstanding, granted |  |  | 2,333,646 |  |
Stock-based compensation expense | 10,443,863 | $ 1,584,283 | $ 13,326,545 | $ 3,511,381 |
Weighted average period to recognize pre-tax compensation expense |  |  | 3 years 6 months |  |
Unrecognized pre-tax compensation expense | $ 89,156,048 |  | $ 89,156,048 |  |
2004 Equity Incentive Plan |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Shares reserve for issuance | 886,598 |  | 886,598 |  |
2004 Equity Incentive Plan | Employee Stock Option |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of options outstanding | 886,598 |  | 886,598 |  |
2013 Incentive Plan |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Shares reserve for issuance | 5,972,038 |  | 5,972,038 |  |
2013 Incentive Plan | Employee Stock Option |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of options outstanding | 2,798,538 |  | 2,798,538 |  |
Number of options outstanding, granted | 306,500 |  | 310,500 |  |
2013 Incentive Plan | Restricted Stock Units (RSUs) |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of restricted stock units outstanding | 2,783,000 |  | 2,783,000 |  |
Number of restricted stock units outstanding, granted | 1,744,071 |  | 1,749,071 |  |
Outside Of Equity Compensation Plans |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Shares reserve for issuance | 1,024,850 |  | 1,024,850 |  |
Outside Of Equity Compensation Plans | Employee Stock Option |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Number of options outstanding, granted | 126,000 |  | 343,000 |  |
Outside Of Equity Compensation Plans | Restricted Stock Units (RSUs) |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Shares reserve for issuance | 591,075 |  | 591,075 |  |
Number of restricted stock units outstanding, granted | 300,000 |  | 584,575 |  |

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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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