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Commitments and Contingencies - Additional Information (Detail) | 12 Months Ended
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Sep. 30, 2017 USD ($) ft² | Sep. 30, 2016 USD ($) ft² | Sep. 30, 2015 USD ($)
Other Commitments [Line Items] |  |  |
Facility rent expense | $ 1,554,000 | $ 926,000 | $ 831,000
Provision for recorded liabilities | 0 |  |
Future commitments | 11,400,000 |  |
Technology License Commitments |  |  |
Other Commitments [Line Items] |  |  |
Milestone payments | 0 | $ 3,000,000 | $ 1,000,000
Corporate Headquarters In Pasadena |  |  |
Other Commitments [Line Items] |  |  |
Rental expense | $ 27,000 |  |
Operating lease expiration month and year | 2019-09 |  |
Percentage of increase in annual rental cost | 3.00% |  |
Office space leases, in square feet | ft² |  | 8,500 |
Research Facility in Madison |  |  |
Other Commitments [Line Items] |  |  |
Operating lease expiration month and year | 2026-09 |  |
Office space leases, in square feet | ft² | 60,000 |  |
Primary tenant improvement allowance accounted for as deferred rent | $ 2,100,000 |  |
Promissory note payable | 2,700,000 |  |
Rental expense including common area maintenance and real estate taxes and payments of principal and interest on the note payable | $ 182,200 |  |
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% |  |
Research Facility in Middleton |  |  |
Other Commitments [Line Items] |  |  |
Rental expense | $ 18,000 |  |
Operating lease expiration month and year | 2016-12 |  |

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