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Income Taxes - Additional Information (Detail) $ in Millions | Sep. 30, 2020 USD ($)
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Income Tax Disclosure [Abstract] |
Valuation allowance against deferred tax assets | 100.00%
Gross federal net operating loss carry forwards | $ 473.0
Gross state net operating loss carry forwards | $ 497.0

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- Definition Federal net operating loss carry forward. + References No definition available. + Details
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Namespace Prefix: | arwr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Percentage of valuation allowance. + References No definition available. + Details
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Namespace Prefix: | arwr_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition State net operating loss carry forwards. + References No definition available. + Details
Name: | arwr_StateNetOperatingLossCarryForwards
Namespace Prefix: | arwr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration