The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717

+ Details

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

- Definition

Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Commitment and contingencies.

+ References

No definition available.

+ Details

Name:	zgh_CommitmentAndContingenciesLineItems
Namespace Prefix:	zgh_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Right-of Way, Pole Attachment, and Other Fees for Access

+ References

No definition available.

+ Details

Name:	zgh_RightOfWayPoleAttachmentAndOtherFeesForAccess
Namespace Prefix:	zgh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=zgh_CreditLetterAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Millions, $ in Millions	12 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2018 CAD ($)	Jun. 30, 2018 USD ($)
Commitment And Contingencies [Line Items]
Lease expense	$ 156.4	$ 68.8	$ 53.1
Expense related to right-of way, pole attachment and other fees for access	$ 43.4	$ 65.1	$ 48.9
Purchase commitments					$ 509.4
Outstanding letters of credit					8.1
Zayo Canada, Inc \| Credit Letter Agreement [Member]
Commitment And Contingencies [Line Items]
Outstanding letters of credit				$ 3.4	2.6
Credit letter agreement limit				$ 5.0	$ 3.8