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Leases - Additional Information (Detail) | 1 Months Ended | 12 Months Ended
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May 31, 2020 ft² | Mar. 31, 2020 USD ($) ft² | Apr. 30, 2019 USD ($) ft² Option | Jan. 31, 2019 ft² | Jan. 31, 2016 ft² | Sep. 30, 2020 USD ($) Option | Sep. 30, 2019 USD ($) | Sep. 30, 2018 USD ($)
Lessee Lease Description [Line Items] |  |  |  |  |  |  |  |
Estimated lease payments |  |  |  |  |  |  | $ 22,385,552 |
Estimated lease payments |  |  |  |  |  | $ 32,311,207 |  |
Operating lease cost |  |  |  |  |  | 2,400,000 | 1,300,000 | $ 1,300,000
Variable lease cost |  |  |  |  |  | 800,000 |  |
Short-term lease cost |  |  |  |  |  | 0 | 0 | 0
Operating lease cash payments |  |  |  |  |  | $ 1,800,000 | $ 1,300,000 | $ 1,300,000
Weighted-average remaining lease term |  |  |  |  |  | 9 years 4 months 24 days |  |
Weighted-average discount rate |  |  |  |  |  | 8.40% |  |
Research Facility in Madison | Wisconsin |  |  |  |  |  |  |  |
Lessee Lease Description [Line Items] |  |  |  |  |  |  |  |
Office space leases, in square feet | ft² |  |  |  |  | 60,000 |  |  |
Lease expiration date | Sep. 30, 2031 |  |  |  | Sep. 30, 2026 |  |  |
Operating lease renewal term |  |  |  |  |  | 5 years |  |
Number of options to renew | Option |  |  |  |  |  | 2 |  |
Additional office space for lease | ft² | 26,000 |  |  | 14,000 |  |  |  |
Operating lease expiration month and year |  |  |  | 2029-09 |  |  |  |
Estimated lease payments |  |  |  |  |  | $ 26,200,000 |  |
Colorado Owner, LLC | Corporate Headquarters In Pasadena | California |  |  |  |  |  |  |  |
Lessee Lease Description [Line Items] |  |  |  |  |  |  |  |
Lease term |  |  | 91 months |  |  |  |  |
Office space leases, in square feet | ft² |  |  | 24,000 |  |  |  |  |
Lease payments, commencement date |  |  | Sep. 30, 2019 |  |  |  |  |
Estimated lease payments |  |  | $ 8,700,000 |  |  |  |  |
Lease expiration date |  |  | Apr. 30, 2027 |  |  |  |  |
Payments for leasehold improvements, net of tenant improvement allowances |  |  | $ 3,500,000 |  |  |  |  |
Operating lease renewal term |  |  | 5 years |  |  |  |  |
Number of options to renew | Option |  |  | 1 |  |  |  |  |
Halozyme, Inc. | California | Sublease Agreement |  |  |  |  |  |  |  |
Lessee Lease Description [Line Items] |  |  |  |  |  |  |  |
Office space leases, in square feet | ft² |  | 21,000 |  |  |  |  |  |
Lease expiration date |  | Jan. 14, 2023 |  |  |  |  |  |
Estimated lease payments |  | $ 2,000,000.0 |  |  |  |  |  |
Sublease commencement date |  | Apr. 01, 2020 |  |  |  |  |  |

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