LEASES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2019	Jul. 01, 2019
LEASES
Package of practical expedients	true
ROU assets	$ 653.0
Lease liabilities	$ 700.1
ASC 842
LEASES
ROU assets		$ 527.6
Lease liabilities		$ 545.1

Indicates (true false) whether practical expedients are elected for not reassessing whether any expired or existing contract is or contains lease, lease classification for expired or existing lease, and initial direct cost for any existing lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984

+ Details

Name:	us-gaap_LeasePracticalExpedientsPackage
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
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

The amount as of the balance sheet date of lease liabilities.

+ References

No definition available.

+ Details

Name:	zgh_LeaseLiabilities
Namespace Prefix:	zgh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount as of the balance sheet date of leases right of use assets.

+ References

No definition available.

+ Details

Name:	zgh_LeasesRightOfUseAsset
Namespace Prefix:	zgh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: