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

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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

Name:	us-gaap_DebtInstrumentFaceAmount
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

Name:	us-gaap_DebtInstrumentInterestRateIncreaseDecrease
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

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
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

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

- Definition

Debt Instrument, Issue Price, Percentage

+ References

No definition available.

+ Details

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

- Definition

Debt Instrument, Repriced Percentage

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=zgh_SeniorNotesDue2027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=zgh_TrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=zgh_TrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=zgh_ElectricLightwaveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=zgh_TermLoan650MillionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Events (Narrative) (Details) - Subsequent Event - USD ($) $ in Millions	Jan. 19, 2017	Jan. 27, 2017
5.75% Senior Notes Due in 2027 [Member]
Subsequent Event [Line Items]
Debt instrument, face amount		$ 800.0
Interest rate		5.75%
Term Loan Facility
Subsequent Event [Line Items]
Debt instrument, face amount	$ 1,850.0
Repriced percentage	99.75%
Term Loan Facility \| Tranche One [Member]
Subsequent Event [Line Items]
Debt instrument, face amount	$ 500.0
Interest rate decrease (basis points)	0.75%
Term Loan Facility \| Tranche One [Member] \| LIBOR
Subsequent Event [Line Items]
Spread on interest rate	2.00%
Term Loan Facility \| Tranche Two [Member]
Subsequent Event [Line Items]
Debt instrument, face amount	$ 1,350.0
Interest rate decrease (basis points)	0.25%
Term Loan Facility \| Tranche Two [Member] \| LIBOR
Subsequent Event [Line Items]
Spread on interest rate	2.50%
Term Loan Facility \| Minimum \| Tranche Two [Member] \| LIBOR
Subsequent Event [Line Items]
Spread on interest rate	1.00%
Electric Lightwave [Member] \| Term Loan Facility \| $650 Million Term Loan [Member]
Subsequent Event [Line Items]
Debt instrument, face amount	$ 650.0
Issue price percentage	99.75%
Electric Lightwave [Member] \| Term Loan Facility \| $650 Million Term Loan [Member] \| LIBOR
Subsequent Event [Line Items]
Spread on interest rate	2.50%
Electric Lightwave [Member] \| Term Loan Facility \| Minimum \| $650 Million Term Loan [Member] \| LIBOR
Subsequent Event [Line Items]
Spread on interest rate	1.00%