Stockholders' Equity	12 Months Ended
Sep. 30, 2018
Equity [Abstract]
Stockholders' Equity	NOTE 6. STOCKHOLDERS’ EQUITY At September 30, 2018, the Company had a total of 150,000,000 shares of capital stock authorized for issuance, consisting of 145,000,000 shares of Common Stock, par value $0.001 per share, and 5,000,000 shares of Preferred Stock, par value $0.001 per share. At September 30, 2018, 88,505,302 shares of Common Stock were outstanding. At September 30, 2018, 8,732,569 shares of Common Stock were reserved for issuance upon exercise of options and vesting of restricted stock units granted or available for grant under Arrowhead’s 2004 Equity Incentive Plan and 2013 Incentive Plan, as well as for inducement grants made to new employees. On January 22, 2018, the Company sold 11,500,000 shares of Common Stock in a fully underwritten public offering, at a public offering price of $5.25 per share. Net proceeds to the Company were approximately $56.6 million after deducting underwriting commissions and discounts and other offering expenses payable by the Company. In October 2018 the Company sold 3,260,869 shares of Common Stock to JJDC at a price of $23.00 per share as part of the JJDC Stock Purchase Agreement discussed further in Note 2 above. The Company received proceeds of $75.0 million.

Stockholders' Equity

12 Months Ended

Sep. 30, 2018

NOTE 6. STOCKHOLDERS’ EQUITY

At September 30, 2018, the Company had a total of 150,000,000 shares of capital stock authorized for issuance, consisting of 145,000,000 shares of Common Stock, par value $0.001 per share, and 5,000,000 shares of Preferred Stock, par value $0.001 per share.

At September 30, 2018, 88,505,302 shares of Common Stock were outstanding. At September 30, 2018, 8,732,569 shares of Common Stock were reserved for issuance upon exercise of options and vesting of restricted stock units granted or available for grant under Arrowhead’s 2004 Equity Incentive Plan and 2013 Incentive Plan, as well as for inducement grants made to new employees.

On January 22, 2018, the Company sold 11,500,000 shares of Common Stock in a fully underwritten public offering, at a public offering price of $5.25 per share. Net proceeds to the Company were approximately $56.6 million after deducting underwriting commissions and discounts and other offering expenses payable by the Company.

In October 2018 the Company sold 3,260,869 shares of Common Stock to JJDC at a price of $23.00 per share as part of the JJDC Stock Purchase Agreement discussed further in Note 2 above. The Company received proceeds of $75.0 million.