Leases (Narratives) (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Lessee Lease Description [Line Items]
Lease option to extend, description	Some lease terms include one or more options to renew.
Lease, existence of option to extend	true
Sublease income	$ 0.6
Product Revenues	$ 3.7	$ 4.0
Minimum
Lessee Lease Description [Line Items]
Sublease term	4 years
Maximum
Lessee Lease Description [Line Items]
Sublease term	6 years
Facilities \| Minimum
Lessee Lease Description [Line Items]
Lease term	1 year
Facilities \| Maximum
Lessee Lease Description [Line Items]
Lease term	9 years
Equipment \| Minimum
Lessee Lease Description [Line Items]
Lease term	1 year
Equipment \| Maximum
Lessee Lease Description [Line Items]
Lease term	6 years
Vehicles \| Minimum
Lessee Lease Description [Line Items]
Lease term	1 year
Vehicles \| Maximum
Lessee Lease Description [Line Items]
Lease term	5 years
Hardware
Lessee Lease Description [Line Items]
Lease term	3 years
Lease termination rights period	60 days
Hardware \| Product
Lessee Lease Description [Line Items]
Product Revenues	$ 3.7	$ 4.0

No definition available.

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Namespace Prefix:	extr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Lessee, operating sublease, term of contract.

+ References

No definition available.

+ Details

Name:	extr_LesseeOperatingSubleaseTermOfContract
Namespace Prefix:	extr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating lease revenue included in product revenue.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether lessee has option to extend operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of terms and conditions of option to extend lessee's operating lease. Includes, but is not limited to, information about option recognized as part of right-of-use asset and lease liability.

+ References

+ Details

Name:	us-gaap_LesseeOperatingLeaseOptionToExtend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of sublease income excluding finance and operating lease expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=77888399&loc=SL77918982-209971

+ Details

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

- Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
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