Organization and Significant Accounting Policies	3 Months Ended
Dec. 31, 2019
Accounting Policies [Abstract]
Organization and Significant Accounting Policies	NOTE 1. ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES Nature of Business and Recent Developments Arrowhead Pharmaceuticals, Inc. develops medicines that treat intractable diseases by silencing the genes that cause them. Using a broad portfolio of RNA chemistries and efficient modes of delivery, Arrowhead therapies trigger the RNA interference mechanism to induce rapid, deep and durable knockdown of target genes. RNA interference, or RNAi, is a mechanism present in living cells that inhibits the expression of a specific gene, thereby affecting the production of a specific protein. Arrowhead’s RNAi-based therapeutics leverage this natural pathway of gene silencing. The Company's pipeline includes ARO-AAT for liver disease associated with alpha-1 antitrypsin deficiency (AATD), ARO-APOC3 for hypertriglyceridemia, ARO-ANG3 for dyslipidemia, ARO-HSD for liver disease, ARO-ENaC for cystic fibrosis, and ARO-HIF2 for renal cell carcinoma. ARO-JNJ1 is being developed for an undisclosed liver-expressed target under a collaboration agreement with Janssen Pharmaceuticals, Inc. (“Janssen”). ARO-HBV (JNJ-3989) for chronic hepatitis B virus was out-licensed to Janssen in October 2018. ARO-LPA (AMG 890)for cardiovascular disease was out-licensed to Amgen Inc. (“Amgen”) in 2016. Arrowhead operates a lab facility in Madison, Wisconsin, where the Company’s research and development activities, including the development of RNAi therapeutics, are based. The Company’s principal executive offices are located in Pasadena, California. During the first quarter of fiscal 2020, the Company has continued to develop its pipeline and partnered candidates. The Company has began dosing in an adaptive design phase 2/3 trial, called SEQUOIA, with the potential to serve as a pivotal registration study of ARO-AAT. The Company also began dosing in its ARO-AAT 2002 study, a pilot open-label, multi-dose Phase 2 study to assess changes in novel histological activity scale in response to ARO-AAT over time in patients with alpha-1 antitrypsin deficiency associated liver disease. The Company also presented new clinical data on its two cardiometabolic candidates, ARO-APOC3 and ARO-ANG3, in two late-breaking oral presentations at the American Heart Association Scientific Sessions 2019. The Company also filed an IND to begin a phase 1b study of ARO-HIF2, and filed a CTA to begin a phase 1 study of ARO-HSD. The Company has continued to work on optimizing its other extra-hepatic preclinical pipeline candidates including ARO-ENaC. The Company’s partnered candidates under its collaboration agreements with Janssen and Amgen also continue to progress. Janssen began dosing patients in a phase 2b triple combination study called REEF-1, designed to enroll up to 450 patients with chronic hepatitis B infection, and in connection with the start of this study Arrowhead earned a $25 million milestone payment under the License Agreement (“Janssen License Agreement”). Janssen has also nominated the first of 3 potential candidates under the Research Collaboration and Option Agreement (“Janssen Collaboration Agreement”), ARO-JNJ1, and the Company is currently performing discovery, optimization and preclinical research and development for this candidate. Under the terms of the Janssen agreements taken together, the Company has received $175 million as an upfront payment, $75 million in the form of an equity investment by JJDC in Arrowhead common stock, two $25 million milestone payments and may receive up to $1.6 billion in development and sales milestones payments for the Janssen License Agreement, and up to $1.9 billion in development and sales milestone payments for the three additional targets covered under the Janssen Collaboration Agreement. The Company is further eligible to receive tiered royalties up to mid teens under the Janssen License Agreement and up to low teens under the Janssen Collaboration Agreement on product sales. The Company’s collaboration agreement with Amgen for AMG 890 (ARO-LPA), (the “Second Collaboration and License Agreement” or “AMG 890 (ARO-LPA) Agreement”), continues to progress. The Company has received $35 million in upfront payments, $21.5 million in the form of an equity investment by Amgen in the Company’s Common Stock, a $10 million milestone payment, and may receive up to $420 million in development, regulatory and sales milestone payments. The Company is eligible to receive up to low double-digit royalties for sales of products under the AMG 890 (ARO-LPA) Agreement. The revenue recognition for these collaboration agreements is discussed further in Note 2 below. Liquidity The Consolidated Financial Statements have been prepared in conformity with the accounting principles generally accepted in the United States of America, which contemplate the continuation of the Company as a going concern. Historically, the Company’s primary source of financing has been through the sale of its securities. Research and development activities have required significant capital investment since the Company’s inception. The Company expects its operations to continue to require cash investment to pursue its research and development goals, including clinical trials and related drug manufacturing. At December 31, 2019, the Company had $461.0 million in cash and cash equivalents (including $1.0 million in restricted cash), $41.0 million in short-term investments, and $26.3 million in long-term investments to fund operations. During the three months ended December 31, 2019, the Company’s cash and investments balance increased by $225.5 million, which was primarily the result of the December 2019 securities offering that generated $250.5 million in net cash proceeds for the Company, as discussed further in Note 6 below. These cash inflows were partially offset by cash outflows related to operating activities. Summary of Significant Accounting Policies There have been no changes to the significant accounting policies disclosed in the Company’s most recent Annual Report on Form 10-K, except as a result of the Financial Accounting Standards Board (FASB)’s Accounting Standards Update (ASU) No. 2016-02, Leases (ASC 842), as discussed below. Leases — The Company determines whether a contract is, or contains, a lease at inception. The Company classifies each of its leases as operating or financing considering factors such as the length of the lease term, the present value of the lease payments, the nature of the asset being leased, and the potential for ownership of the asset to transfer during the lease term. Leases with terms greater than one-year are recognized on the Consolidated Balance Sheets as Right-of-use assets and Lease liabilities and are measured at the present value of the fixed payments due over the expected lease term less the present value of any incentives, rebates or abatements expected to be received from the lessor. Options to extend a lease are typically excluded from the expected lease term as the exercise of the option is typically not reasonably certain. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis an amount equal to the lease payments over a similar term and in a similar economic environment. The Company records expense to recognize fixed lease payments on a straight-line basis over the expected lease term. Costs determined to be variable and not based on an index or rate are not included in the measurement of the lease liability and are expensed as incurred. Recent Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-02, Leases (Topic ASC 842). Under ASC 842, lessees are required to recognize a right-of-use asset and a right-of-use lease liability for virtually all leases other than those that meet the definition of a short-term lease. For income statement purposes, a dual model was retained, requiring leases to be classified as either operating or finance. Operating leases will result in straight-line expense while finance leases will result in a front-loaded expense pattern (similar to current capital leases). The Company adopted this standard effective October 1, 2019 and elected the package of three practical expedients that permits an entity to a) not reassess whether expired or existing contracts contain leases, b) not reassess lease classification for existing or expired leases, and c) not consider whether previously capitalized initial direct costs would be appropriate under the new standard. At December 31, 2019, the Company has recorded right-of-use assets of $10.4 million and right-of-use liabilities of $14.8 million on its Consolidated Balance Sheets for its research and development facility lease in Madison, Wisconsin, and its corporate headquarters lease in Pasadena, California, as discussed further in Note 8 below. The adoption of this standard did not have a material impact on the Company’s Consolidated Statement of Comprehensive Income (Loss) and the Company’s Consolidated Statement of Cash Flows. In November 2018, the FASB issued ASU No. 2018-18 Collaborative Arrangements (Topic 808). This update provides clarification on the interaction between Revenue Recognition (Topic 606) and Collaborative Arrangements (Topic 808) including the alignment of unit of account guidance between the two topics. ASU 2018-18 becomes effective for the Company in the first quarter of fiscal 2021 with early adoption permitted. The Company does not expect the adoption of this update to have a material effect on its Consolidated Financial Statements.

Organization and Significant Accounting Policies

3 Months Ended

Dec. 31, 2019

Organization and Significant Accounting Policies

NOTE 1. ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES

Nature of Business and Recent Developments

Arrowhead Pharmaceuticals, Inc. develops medicines that treat intractable diseases by silencing the genes that cause them. Using a broad portfolio of RNA chemistries and efficient modes of delivery, Arrowhead therapies trigger the RNA interference mechanism to induce rapid, deep and durable knockdown of target genes. RNA interference, or RNAi, is a mechanism present in living cells that inhibits the expression of a specific gene, thereby affecting the production of a specific protein. Arrowhead’s RNAi-based therapeutics leverage this natural pathway of gene silencing. The Company's pipeline includes ARO-AAT for liver disease associated with alpha-1 antitrypsin deficiency (AATD), ARO-APOC3 for hypertriglyceridemia, ARO-ANG3 for dyslipidemia, ARO-HSD for liver disease, ARO-ENaC for cystic fibrosis, and ARO-HIF2 for renal cell carcinoma. ARO-JNJ1 is being developed for an undisclosed liver-expressed target under a collaboration agreement with Janssen Pharmaceuticals, Inc. (“Janssen”). ARO-HBV (JNJ-3989) for chronic hepatitis B virus was out-licensed to Janssen in October 2018. ARO-LPA (AMG 890)for cardiovascular disease was out-licensed to Amgen Inc. (“Amgen”) in 2016.

Arrowhead operates a lab facility in Madison, Wisconsin, where the Company’s research and development activities, including the development of RNAi therapeutics, are based. The Company’s principal executive offices are located in Pasadena, California.

During the first quarter of fiscal 2020, the Company has continued to develop its pipeline and partnered candidates. The Company has began dosing in an adaptive design phase 2/3 trial, called SEQUOIA, with the potential to serve as a pivotal registration study of ARO-AAT. The Company also began dosing in its ARO-AAT 2002 study, a pilot open-label, multi-dose Phase 2 study to assess changes in novel histological activity scale in response to ARO-AAT over time in patients with alpha-1 antitrypsin deficiency associated liver disease. The Company also presented new clinical data on its two cardiometabolic candidates, ARO-APOC3 and ARO-ANG3, in two late-breaking oral presentations at the American Heart Association Scientific Sessions 2019. The Company also filed an IND to begin a phase 1b study of ARO-HIF2, and filed a CTA to begin a phase 1 study of ARO-HSD. The Company has continued to work on optimizing its other extra-hepatic preclinical pipeline candidates including ARO-ENaC.

The Company’s partnered candidates under its collaboration agreements with Janssen and Amgen also continue to progress. Janssen began dosing patients in a phase 2b triple combination study called REEF-1, designed to enroll up to 450 patients with chronic hepatitis B infection, and in connection with the start of this study Arrowhead earned a $25 million milestone payment under the License Agreement (“Janssen License Agreement”). Janssen has also nominated the first of 3 potential candidates under the Research Collaboration and Option Agreement (“Janssen Collaboration Agreement”), ARO-JNJ1, and the Company is currently performing discovery, optimization and preclinical research and development for this candidate. Under the terms of the Janssen agreements taken together, the Company has received $175 million as an upfront payment, $75 million in the form of an equity investment by JJDC in Arrowhead common stock, two $25 million milestone payments and may receive up to $1.6 billion in development and sales milestones payments for the Janssen License Agreement, and up to $1.9 billion in development and sales milestone payments for the three additional targets covered under the Janssen Collaboration Agreement. The Company is further eligible to receive tiered royalties up to mid teens under the Janssen License Agreement and up to low teens under the Janssen Collaboration Agreement on product sales. The Company’s collaboration agreement with Amgen for AMG 890 (ARO-LPA), (the “Second Collaboration and License Agreement” or “AMG 890 (ARO-LPA) Agreement”), continues to progress. The Company has received $35 million in upfront payments, $21.5 million in the form of an equity investment by Amgen in the Company’s Common Stock, a $10 million milestone payment, and may receive up to $420 million in development, regulatory and sales milestone payments. The Company is eligible to receive up to low double-digit royalties for sales of products under the AMG 890 (ARO-LPA) Agreement.

The revenue recognition for these collaboration agreements is discussed further in Note 2 below.

Liquidity

The Consolidated Financial Statements have been prepared in conformity with the accounting principles generally accepted in the United States of America, which contemplate the continuation of the Company as a going concern. Historically, the Company’s primary source of financing has been through the sale of its securities. Research and development activities have required significant capital investment since the Company’s inception. The Company expects its operations to continue to require cash investment to pursue its research and development goals, including clinical trials and related drug manufacturing.

At December 31, 2019, the Company had $461.0 million in cash and cash equivalents (including $1.0 million in restricted cash), $41.0 million in short-term investments, and $26.3 million in long-term investments to fund operations. During the three months ended December 31, 2019, the Company’s cash and investments balance increased by $225.5 million, which was primarily the result of the December 2019 securities offering that generated $250.5 million in net cash proceeds for the Company, as discussed further in Note 6 below. These cash inflows were partially offset by cash outflows related to operating activities.

Summary of Significant Accounting Policies

There have been no changes to the significant accounting policies disclosed in the Company’s most recent Annual Report on Form 10-K, except as a result of the Financial Accounting Standards Board (FASB)’s Accounting Standards Update (ASU) No. 2016-02, Leases (ASC 842), as discussed below.

Leases — The Company determines whether a contract is, or contains, a lease at inception. The Company classifies each of its leases as operating or financing considering factors such as the length of the lease term, the present value of the lease payments, the nature of the asset being leased, and the potential for ownership of the asset to transfer during the lease term. Leases with terms greater than one-year are recognized on the Consolidated Balance Sheets as Right-of-use assets and Lease liabilities and are measured at the present value of the fixed payments due over the expected lease term less the present value of any incentives, rebates or abatements expected to be received from the lessor. Options to extend a lease are typically excluded from the expected lease term as the exercise of the option is typically not reasonably certain. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis an amount equal to the lease payments over a similar term and in a similar economic environment. The Company records expense to recognize fixed lease payments on a straight-line basis over the expected lease term. Costs determined to be variable and not based on an index or rate are not included in the measurement of the lease liability and are expensed as incurred.

Recent Accounting Pronouncements

In March 2016, the FASB issued ASU No. 2016-02, Leases (Topic ASC 842). Under ASC 842, lessees are required to recognize a right-of-use asset and a right-of-use lease liability for virtually all leases other than those that meet the definition of a short-term lease. For income statement purposes, a dual model was retained, requiring leases to be classified as either operating or finance. Operating leases will result in straight-line expense while finance leases will result in a front-loaded expense pattern (similar to current capital leases). The Company adopted this standard effective October 1, 2019 and elected the package of three practical expedients that permits an entity to a) not reassess whether expired or existing contracts contain leases, b) not reassess lease classification for existing or expired leases, and c) not consider whether previously capitalized initial direct costs would be appropriate under the new standard. At December 31, 2019, the Company has recorded right-of-use assets of $10.4 million and right-of-use liabilities of $14.8 million on its Consolidated Balance Sheets for its research and development facility lease in Madison, Wisconsin, and its corporate headquarters lease in Pasadena, California, as discussed further in Note 8 below. The adoption of this standard did not have a material impact on the Company’s Consolidated Statement of Comprehensive Income (Loss) and the Company’s Consolidated Statement of Cash Flows.

In November 2018, the FASB issued ASU No. 2018-18 Collaborative Arrangements (Topic 808). This update provides clarification on the interaction between Revenue Recognition (Topic 606) and Collaborative Arrangements (Topic 808) including the alignment of unit of account guidance between the two topics. ASU 2018-18 becomes effective for the Company in the first quarter of fiscal 2021 with early adoption permitted. The Company does not expect the adoption of this update to have a material effect on its Consolidated Financial Statements.