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Subsequent Events - Additional Information (Detail) |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Oct. 03, 2018 | Nov. 30, 2018 USD ($) | Oct. 31, 2018 USD ($) Target $ / shares shares | Sep. 30, 2018 USD ($) $ / shares | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($)
Subsequent Event [Line Items] |  |  |  |  |  |
Stock issued, price per share | $ / shares |  |  |  | $ 5.25 |  |
Proceeds from the issuance of common stock |  |  |  | $ 56,585,035 | $ 12,419,119 | $ 52,231,433
Subsequent Event | Common Stock Purchase Agreement | Janssen |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Agreement date | Oct. 03, 2018 |  |  |  |  |
Subsequent Event | Common Stock Purchase Agreement | JJDC |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Shares issued | shares |  |  | 3,260,869 |  |  |
Stock issued, price per share | $ / shares |  |  | $ 23.00 |  |  |
Proceeds from the issuance of common stock |  |  | $ 75,000,000 |  |  |
Subsequent Event | License Agreement | Janssen |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Agreement date | Oct. 03, 2018 |  |  |  |  |
Subsequent Event | License Agreement | Janssen | Maximum |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Development and sales milestone payments |  |  | 1,600,000,000 |  |  |
Subsequent Event | Research Collaboration and Option Agreement | Janssen |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Agreement date | Oct. 03, 2018 |  |  |  |  |
Subsequent Event | Collaboration and License agreements | JJDC |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Cash received as due under collaboration agreement |  | $ 175,000,000 | 175,000,000 |  |  |
Proceeds from the issuance of common stock |  |  | $ 75,000,000 |  |  |
Subsequent Event | Collaboration Agreement | Janssen |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Number of additional targets for development and sales milestone payments | Target |  |  | 3 |  |  |
Subsequent Event | Collaboration Agreement | Janssen | Maximum |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Development and sales milestone payments |  |  | $ 1,900,000,000 |  |  |

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