Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	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%