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Leases - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended		113 Months Ended
	Aug. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012
Component of Operating Other Cost and Expense [Line Items]
Rental expense	$ 13,000			$ 4,125,485
Lease term	5 years
Percentage of increase in annual rental cost	3.00%
Rental expenses include common area maintenance and real estate taxes		13,000
Utilities costs		16,000
Increase in total monthly expenditures		72,000
Facility and equipment rent expense		480,000	162,000
Roche [Member]
Component of Operating Other Cost and Expense [Line Items]
Rental expense		22,000
Payments under a capitalized lease		$ 21,000

X

- Definition

Capital Lease Term Of Lease

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

X

- Definition

Facility and equipment rent expense.

+ References

No definition available.

+ Details

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Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Increase in monthly expenditure due to utilities costs.

+ References

No definition available.

+ Details

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Namespace Prefix:	arwr_
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Balance Type:	debit
Period Type:	duration

X

- Definition

Other rental expenses.

+ References

No definition available.

+ Details

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Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Payments under capital lease.

+ References

No definition available.

+ Details

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Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Percentage Of Increase In Annual Rental Cost

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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X

- Details

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X

- Definition

Rental expense incurred for leased assets including furniture and equipment which has not been recognized in costs and expenses applicable to sales and revenues; for example, cost of goods sold or other operating costs and expenses.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Utilities costs incurred during the reporting period for services, such as water, sewer, gas, electricity and telephone required to operate a building.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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