Note 13 - Licenses, Royalty, Collaborative and Contractual Arrangements - Components of Revenues From Royalties, Collaborative and Contractual Agreements (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Royalty revenue		$ 0.1	$ 5.7	$ 9.1
Non-cash royalty revenue related to the sale of future royalties	0.1		3.2	0.2
Total revenue	0.1	0.1	8.9	9.3
Relenza [Member]
Royalty revenue		$ 0.1	2.5	4.8
Inavir [Member]
Royalty revenue			$ 3.2	$ 4.3

Non-cash revenue earned for sales of future royalties from the leasing or otherwise lending to a third party the entity's rights or title to certain property. Examples of property from which royalties may be derived include patents and oil and mineral rights.

No definition available.

+ Details

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Namespace Prefix:	avir_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ 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 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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- Definition

Revenue earned during the period from the leasing or otherwise lending to a third party the entity's rights or title to certain property. Royalty revenue is derived from a percentage or stated amount of sales proceeds or revenue generated by the third party using the entity's property. Examples of property from which royalties may be derived include patents and oil and mineral rights.

+ 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 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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Balance Type:	credit
Period Type:	duration

- Details

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- Details

Name:	us-gaap_ProductOrServiceAxis=avir_InavirMember
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Period Type: