Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

Incremental percentage increase (decrease) in the stated rate on a debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage price of notes.

+ References

No definition available.

+ Details

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Namespace Prefix:	zgh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_LongtermDebtTypeAxis=zgh_TermLoanFacilityMember
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Balance Type:
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- Details

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- Details

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Namespace Prefix:
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- Details

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Subsequent Events (Details) - USD ($) $ in Millions	Jul. 20, 2017	Jul. 05, 2017	Jul. 22, 2016	Jun. 30, 2017	Apr. 10, 2017	Jan. 27, 2017	Jan. 19, 2017	Jun. 30, 2016
5.75% Senior Unsecured Notes due 2027 [Member]
Subsequent Event [Line Items]
Aggregate principal amount					$ 550.0	$ 800.0
Interest rate					5.75%	5.75%
Term Loan Facility
Subsequent Event [Line Items]
Aggregate principal amount							$ 1,850.0
Interest rate decrease (basis point)			75.00%
Term Loan Facility \| LIBOR
Subsequent Event [Line Items]
Basis spread			2.75%
Unsecured Notes \| 5.75% Senior Unsecured Notes due 2027 [Member]
Subsequent Event [Line Items]
Interest rate				5.75%				5.75%
Subsequent Event [Member] \| Private offering \| LIBOR
Subsequent Event [Line Items]
Basis spread	1.00%
Subsequent Event [Member] \| Private offering \| 5.75% Senior Unsecured Notes due 2027 [Member]
Subsequent Event [Line Items]
Aggregate principal amount		$ 300.0
Interest rate		5.75%
Subsequent Event [Member] \| Term Loan Facility \| Private offering
Subsequent Event [Line Items]
Aggregate principal amount		$ 1,618.1
Basis spread	2.25%
Subsequent Event [Member] \| Unsecured Notes \| Private offering
Subsequent Event [Line Items]
Aggregate principal amount		$ 1,650.0
Percentage price of notes		104.25%