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Commitments and Contingencies - Additional Information (Detail) | 12 Months Ended
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Sep. 30, 2018 USD ($) ft² | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($)
Other Commitments [Line Items] |  |  |
Facility rent expense | $ 1,288,000 | $ 1,441,000 | $ 839,000
Provision for recorded liabilities | 0 |  |
Future commitments | 27,500,000 |  |
Commitments expected to be incurred in fiscal 2019 | 20,100,000 |  |
Commitments expected to be incurred beyond fiscal 2019 | 7,400,000 |  |
Technology License Commitments |  |  |
Other Commitments [Line Items] |  |  |
Milestone payments | $ 0 | $ 0 | $ 3,000,000
Corporate Headquarters In Pasadena |  |  |
Other Commitments [Line Items] |  |  |
Office space leases, in square feet | ft² | 8,500 |  |
Operating lease expiration month and year | 2019-09 |  |
Rental expense | $ 28,100 |  |
Percentage of increase in annual rental cost | 3.00% |  |
Research Facility in Madison |  |  |
Other Commitments [Line Items] |  |  |
Office space leases, in square feet | ft² | 60,000 |  |
Operating lease expiration month and year | 2026-09 |  |
Primary tenant improvement allowance accounted for as deferred rent | $ 2,100,000 |  |
Promissory note payable | 2,700,000 |  |
Rental expense including payments of principal and interest on the note payable | $ 186,300 |  |
Percentage of increase in annual rental cost excluding principal and interest on the note payable | 2.50% |  |
Promissory notes payable amortized term | 10 years |  |
Promissory note commencement date | Oct. 01, 2016 |  |
Promissory note interest rate | 7.10% |  |

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