Subsequent Events	12 Months Ended
Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	NOTE 14. SUBSEQUENT EVENTS Exclusive License and Co-Funding Agreement with Takeda Pharmaceuticals U.S.A., Inc. On October 7, 2020, the Company entered into an Exclusive License and Co-Funding Agreement (the “Takeda License Agreement”) with Takeda Pharmaceuticals U.S.A., Inc. (“Takeda”). Under the Takeda License Agreement, Takeda and the Company will co-develop the Company’s ARO-AAT program, the Company’s second-generation subcutaneously administered RNAi therapeutic candidate being developed as a treatment for liver disease associated with alpha-1 antitrypsin deficiency. Within the United States, ARO-AAT, if approved, will be co-commercialized under a 50/50 profit sharing structure. Outside the United States, Takeda will lead the global commercialization strategy and receive an exclusive license to commercialize ARO-AAT with the Company eligible to receive tiered royalties of 20% to 25% on net sales. The Company will receive $300.0 million as an upfront payment and is eligible to receive potential development, regulatory and commercial milestones of up to $740.0 million. Corporate Headquarters Lease Expansion On October 23, 2020, the Company signed a lease expansion to add an additional 24,434 square feet of office space for the Company’s corporate headquarters in Pasadena, CA. The lease commencement date is expected to be July 2021, after certain leasehold improvements are completed, and the lease expires in April 2027. The lease payments over the life of lease total $7.3 million. The Company anticipates paying approximately $4.0 million of leasehold improvements, net of tenant improvement allowances. The increased capacity of this additional office space compared to the Company’s current corporate headquarters will accommodate increased personnel as the Company’s pipeline of drug candidates expands and moves closer to market.

Subsequent Events

12 Months Ended

Sep. 30, 2020

NOTE 14. SUBSEQUENT EVENTS

Exclusive License and Co-Funding Agreement with Takeda Pharmaceuticals U.S.A., Inc.

On October 7, 2020, the Company entered into an Exclusive License and Co-Funding Agreement (the “Takeda License Agreement”) with Takeda Pharmaceuticals U.S.A., Inc. (“Takeda”). Under the Takeda License Agreement, Takeda and the Company will co-develop the Company’s ARO-AAT program, the Company’s second-generation subcutaneously administered RNAi therapeutic candidate being developed as a treatment for liver disease associated with alpha-1 antitrypsin deficiency. Within the United States, ARO-AAT, if approved, will be co-commercialized under a 50/50 profit sharing structure. Outside the United States, Takeda will lead the global commercialization strategy and receive an exclusive license to commercialize ARO-AAT with the Company eligible to receive tiered royalties of 20% to 25% on net sales. The Company will receive $300.0 million as an upfront payment and is eligible to receive potential development, regulatory and commercial milestones of up to $740.0 million.

Corporate Headquarters Lease Expansion

On October 23, 2020, the Company signed a lease expansion to add an additional 24,434 square feet of office space for the Company’s corporate headquarters in Pasadena, CA. The lease commencement date is expected to be July 2021, after certain leasehold improvements are completed, and the lease expires in April 2027. The lease payments over the life of lease total $7.3 million. The Company anticipates paying approximately $4.0 million of leasehold improvements, net of tenant improvement allowances. The increased capacity of this additional office space compared to the Company’s current corporate headquarters will accommodate increased personnel as the Company’s pipeline of drug candidates expands and moves closer to market.