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Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Milestone payment receivable at start of phase two Milestone Payment Receivable At Start Of Phase Two Milestone payment receivable at start of phase two. Property and equipment, gross Property, Plant and Equipment, Gross Tax increment financing award Tax Increment Financing Award Tax Increment Financing Award Financial Instruments [Domain] Financial Instruments [Domain] Statistical Measurement Statistical Measurement [Domain] Exercise of stock options (in shares) Exercised (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Share-based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] Additional paid-in capital Additional Paid in Capital, Common Stock Net loss attributable to Arrowhead Pharmaceuticals, Inc. 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Schedule of Company's Current Pipeline Schedule of Current Products [Table Text Block] Schedule of Current Products Interest in joint venture Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Janssen Janssen Pharmaceuticals Incorporation [Member] Janssen Pharmaceuticals, Incorporation. 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Entity Registrant Name Entity Registrant Name Patents Patents [Member] Entity Address, City or Town Entity Address, City or Town Commercial milestone payments at first commercial sale Commercial Milestone Payments At First Commercial Sale Commercial milestone payments at first commercial sale. 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Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Additional remaining development regulatory and sales milestones payments Additional Remaining Development Regulatory And Sales Milestones Payments Additional remaining development regulatory and sales milestones payments. 2021 Incentive Plan Two Thousand Twenty One Incentive Plan [Member] Two thousand twenty one incentive plan. Trading Symbol Trading Symbol Entity File Number Entity File Number Intangible Assets Intangible Assets Disclosure [Text Block] 2027 Finite-Lived Intangible Asset, Expected Amortization, Year Four Deferred revenue, net of current portion Contract with Customer, Liability, Noncurrent Leasehold improvements Leasehold Improvements, Gross Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Money market instruments Cash and Cash Equivalents, Fair Value Disclosure License Agreement License Agreement [Member] License agreement. Proceeds from the sale of future royalties Proceeds from Contributed Capital Accounts payable Increase (Decrease) in Accounts Payable Visirna Therapeutics, Inc. Visirna Therapeutics, Inc. [Member] Visirna Therapeutics, Inc. Organization and Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Milestone payment Milestone Payment Earned Milestone payment earned. Long-term investments, Held to maturity, Fair Value Debt Securities, Held-to-Maturity, Fair Value, Noncurrent Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Amortization expense Amortization of Intangible Assets Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Basic (in dollars per share) Earnings Per Share, Basic 2026 Lessee, Operating Lease, Liability, to be Paid, Year Three Construction in progress Construction in Progress, Gross Schedule Of Held To Maturity Securities And Marketable Securities [Table] Schedule Of Held To Maturity Securities And Marketable Securities [Table] Schedule of held to maturity securities and marketable securities. 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Total Arrowhead Pharmaceuticals, Inc. stockholders’ equity Stockholders' Equity Attributable to Parent BEGINNING OF PERIOD END OF PERIOD Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Prepaid expenses Prepaid Expense, Current Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Entity Interactive Data Current Entity Interactive Data Current Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Milestone payment receivable upon achievement of phase two and first patient dosed in phase three Milestone Payment Receivable Upon Achievement Of Phase Two And First Patient Dosed In Phase Three Milestone payment receivable upon achievement of phase two and first patient dosed in phase three. 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Total Lease, Cost Collaboration And License Agreements [Abstract] Collaboration And License Agreements [Abstract] Collaboration and license agreements. Common Stock Common Stock [Member] Schedule of Lease Assets and Liabilities and Lease Cost Lease, Cost [Table Text Block] Common stock, share reserve for issuance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant Statement [Table] Statement [Table] Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Operating lease renewal term Lessee, Operating Lease, Renewal Term Schedule Of Held To Maturity Securities And Marketable Securities [Line Items] Schedule Of Held To Maturity Securities And Marketable Securities [Line Items] Schedule of held to maturity securities and marketable securities. Document Quarterly Report Document Quarterly Report Current assets: Assets, Current [Abstract] Liability related to the sale of future royalties Liability, Sale of Future Royalties Liability, Sale of Future Royalties Payments for leasehold improvements, net of tenant improvement allowances Payments Of Leasehold Improvements Net Of Tenant Improvement Allowances Payments of leasehold improvements net of tenant improvement allowances. Lease liabilities, net of current portion Operating Lease, Liability, Noncurrent Organization And Significant Accounting Policies [Table] Organization And Significant Accounting Policies [Table] Organization and significant accounting policies. 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Takeda License Agreement Takeda Pharmaceuticals United States Of America Incorporated [Member] Takeda Pharmaceuticals United States of America Incorporated. CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Statement [Line Items] Statement [Line Items] Share-based payment award (in shares) Beginning of period (in shares) End of period (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Short-term investments, Held to maturity, Fair Value Debt Securities, Held-to-Maturity, Fair Value, Current Total other income Nonoperating Income (Expense) Fair Value Hierarchy and NAV Fair Value Hierarchy and NAV [Axis] Gross Carrying Amount Finite-Lived Intangible Assets, Gross California CALIFORNIA Right-of-use assets Operating Lease, Right-of-Use Asset Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Horizon Therapeutics Ireland DAC Horizon Therapeutics Ireland D A C [Member] Horizon Therapeutics Ireland DAC. Liability Related to the Sale of Future Royalties Liability Related To The Sale Of Future Royalties [Text Block] Liability Related To The Sale Of Future Royalties Document Transition Report Document Transition Report Local Phone Number Local Phone Number Summarized Information about Stock Options Share-Based Payment Arrangement, Option, Activity [Table Text Block] Operating loss Operating Income (Loss) Summary of Awards Outstanding Share-Based Payment Arrangement, Activity [Table Text Block] Upfront milestone payment received Upfront Milestone Payment Received Upfront milestone payment received. Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Milestone payments Milestone Payments Milestone payments. Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Weighted-average shares used in calculating Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] Adjustments to reconcile net loss to net cash flow from operating activities Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Income tax expense Income Tax Expense (Benefit) Geographical [Domain] Geographical [Domain] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share 2027 Lessee, Operating Lease, Liability, to be Paid, Year Four Income Statement [Abstract] Income Statement [Abstract] Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross Additional Paid-In Capital Additional Paid-in Capital [Member] License Licensing Agreements [Member] Balance Sheet Location Balance Sheet Location [Domain] Document Fiscal Period Focus Document Fiscal Period Focus Intrinsic value of options exercised Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Less: Accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Computers, software, office equipment and furniture Computers Software Office Equipment And Furniture Gross Computers, software, office equipment and furniture gross. Liability Related To The Sale Of Future Royalties [Abstract] Liability Related To The Sale Of Future Royalties Collaborative Arrangement and Arrangement Other than Collaborative Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Novartis Novartis [Member] Novartis. Short-term investments, Held to maturity, Gross Unrealized Losses Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss, Current Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss, Current Common stock, $0.001 par value: Authorized 145,000 shares; issued and outstanding 106,140 and 105,960 shares Common Stock, Value, Issued Increase in cash and investments Increase (Decrease) In Cash And Investments Increase decrease in cash and investments. License and Co-Funding Agreement License And Co Funding Agreement [Member] License and co-funding agreement. Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Common stock - restricted stock units vesting (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Gross Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Aggregate Intrinsic Value, Exercisable Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Short-term lease cost Short-Term Lease, Cost Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Foreign currency translation adjustments Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Organization And Significant Accounting Policies [Line Items] Organization And Significant Accounting Policies [Line Items] Organization and significant accounting policies. 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Income Statement Location [Domain] Income Statement Location [Domain] Royalty payment threshold Royalty Payment Threshold Royalty Payment Threshold Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Amendment Flag Amendment Flag Facilities Facilities [Member] Facilities. Useful Lives Finite-Lived Intangible Asset, Useful Life Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Operating lease cost Operating Lease, Cost ARO-XDH A R O X D H Agreement [Member] ARO-XDH Agreement. Non-cash interest expense on liability related to the sale of future royalties Non-Cash Interest Expense, Liability Related to Sale of Future Royalties Non-Cash Interest Expense, Liability Related to Sale of Future Royalties Entity Current Reporting Status Entity Current Reporting Status Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Other assets Other Assets, Noncurrent Number of Options Outstanding, Exercisable (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number Depreciation and amortization expense for property and equipment Depreciation, Depletion and Amortization Royalty Pharma Agreement Royalty Pharma Agreement [Member] Royalty Pharma Agreement Common Stock Purchase Agreement Common Stock Purchase Agreement [Member] Common stock purchase agreement. Lease term Lessee, Operating Lease, Term of Contract Counterparty Name Counterparty Name [Axis] Number of options outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Schedule Of Stock By Class [Table] Schedule of Stock by Class [Table] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Effect of exchange rate on cash, cash equivalents and restricted cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net Verona Technology Park Verona Technology Park [Member] Verona technology park. Operating cash flows from operating leases Operating Lease, Payments Schedule of Intangible Assets Future Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Lease Assets and Liabilities Assets and Liabilities, Lessee [Abstract] Employee Stock Option Share-Based Payment Arrangement, Option [Member] Amgen Amgen Incorporated [Member] Amgen Incorporated. Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Other income (expense), net Other Nonoperating Income (Expense) Balance Sheet Location Balance Sheet Location [Axis] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Total operating expenses Operating Expenses Maximum Maximum [Member] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Cash, cash equivalents and restricted cash Cash and Cash Equivalents, at Carrying Value Deferred revenue Increase (Decrease) in Contract with Customer, Liability Total current assets Assets, Current Income taxes (paid) refunded Income Taxes Paid, Net Entity Small Business Entity Small Business Other Commitments [Table] Other Commitments [Table] Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding Measurement Frequency Measurement Frequency [Domain] Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Deferred Revenue Deferred Revenue [Member] Deferred revenue. Intangible assets, net Net Carrying Amount Finite-Lived Intangible Assets, Net Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward] Property and Equipment Property, Plant and Equipment Disclosure [Text Block] 2028 and thereafter Lessee Operating Lease Liability Payments Due Year Five And After Year Five Lessee operating lease liability payments due year five and after year five. 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Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Two Research equipment Research Equipment Gross Research equipment gross. LIABILITIES, NONCONTROLLING INTEREST AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Granted (in dollars per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Percentage of eligible to receive tiered royalties on net sales Percentage Of Eligible To Receive Tiered Royalties On Net Sales Percentage of eligible to receive tiered royalties on net sales. Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Land purchased, number of acres Number Of Acres Of Land Purchased Number of acres of land purchased. 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Schedule of Operating Leased Assets [Table] Schedule of Operating Leased Assets [Table] Colorado Owner, LLC Colorado Owner L L C [Member] Colorado Owner, LLC. Shares reserve for issuance (in shares) Common Stock, Capital Shares Reserved for Future Issuance Long-term liabilities: Liabilities, Noncurrent [Abstract] Cover [Abstract] Cover [Abstract] Level 3 Fair Value, Inputs, Level 3 [Member] Number of agreements Number Of Agreements Number of agreements. 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Less imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Finite Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Diluted (in dollars per share) Earnings Per Share, Diluted Sale of Stock Sale of Stock [Domain] Schedule of Shares of Common Stock and Preferred Stock Schedule of Stock by Class [Table Text Block] Stock-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Milestone payment receivable upon receipt of royalty payments Milestone Payment Receivable, Upon Receipt Of Royalty Payments Milestone Payment Receivable, Upon Receipt Of Royalty Payments Total current liabilities Liabilities, Current 2025 Lessee, Operating Lease, Liability, to be Paid, Year Two Other current assets Other Assets, Current Summary of Share Activity Related to RSUs Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Collaboration and License agreements Collaboration And License Agreement [Member] Collaboration and license agreements. Corporate debt securities Corporate Debt Securities [Member] Other income (expense): Nonoperating Income (Expense) [Abstract] Summary of Maturities of Operating Lease Liabilities on an Undiscounted Basis Lessee, Operating Lease, Liability, Maturity [Table Text Block] Entity Address, Address Line Two Entity Address, Address Line Two Entity Address, Address Line One Entity Address, Address Line One JNJ-75220795 (ARO-JNJ1) J N J75220795 A R O J N J1 [Member] JNJ 75220795 ARO JNJ1. Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Equity [Abstract] Equity [Abstract] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Entity Tax Identification Number Entity Tax Identification Number Number of shares authorized (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized Milestone payment receivable Milestone Payment Receivable Milestone Payment Receivable Wisconsin WISCONSIN JJDC Johnson And Johnson Innovation J J D C Incorporation [Member] Johnson and Johnson Innovation-JJDC, Incorporation. 2023 (remainder) Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year Contract assets Contract with Customer, Asset, after Allowance for Credit Loss, Current Consolidated Entities [Domain] Consolidated Entities [Domain] Research and development Research and Development Expense (Excluding Acquired in Process Cost) Thereafter Finite-Lived Intangible Asset, Expected Amortization, after Year Four Finite-Lived Intangible Asset, Expected Amortization, after Year Four Net increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Accrued Expenses Accrued Liabilities [Member] Entity Central Index Key Entity Central Index Key Estimated payments for operating expenses Estimated Payments For Operating Expenses Year One Estimated payments for operating expenses year one. Measurement Frequency Measurement Frequency [Axis] Weighted- Average Grant Date Fair Value Per Share Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Finite-Lived Intangible Assets by Major Class Finite-Lived Intangible Assets by Major Class [Axis] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Collaboration and License Agreements Collaborative Arrangement Disclosure [Text Block] Entity [Domain] Entity [Domain] City Area Code City Area Code General and administrative General and Administrative Expense ASSETS Assets [Abstract] Other Commitments [Line Items] Other Commitments [Line Items] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Sale of Stock Sale of Stock [Axis] Laboratory and Office Facility Laboratory And Office Facility [Member] Laboratory and office facility. CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] CASH, CASH EQUIVALENTS AND RESTRICTED CASH: Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations [Abstract] Stock-based compensation Share-Based Payment Arrangement, Noncash Expense Research Facility in Madison Research Facility In Madison [Member] Research facility in Madison. Long-term investments, Held to maturity, Gross Unrealized Gains Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain, Noncurrent Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain, Noncurrent Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Research and development Research and Development Expense [Member] 2024 Finite-Lived Intangible Asset, Expected Amortization, Year One