Leases - Additional Information (Detail)	1 Months Ended					12 Months Ended
	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