Aggregate payments of multiemployer pension plan withdrawal liability according to actuarial calculation.

No definition available.

Name:	gk_Aggregatepaymentsofmultiemployerpensionplanwithdrawalliability
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined benefit plan Period of payment of withdrawal liability.

+ References

No definition available.

+ Details

Name:	gk_DefinedBenefitPlanPeriodOfPaymentOfWithdrawalLiability
Namespace Prefix:	gk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate payments of multiemployer plan withdrawal liability according to demand notice provided by the plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Per the demand notice received by the plan, the amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

No definition available.

+ Details

Name:	gk_Demandnoticemultiemployerplanwithdrawalliability
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Payments made to the Central States multiemployer pension fund during the period.

+ References

No definition available.

+ Details

Name:	gk_MultiemployerPensionPaymentsCentralStates
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of MEPPs where we have determined that the amounts are reasonable and correctly calculated and the withdrawal liabilities are within established reserves.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of multiemployer pension plans in which we participate, not including the Central States Fund, and are currently negotiating to withdraw from.

+ References

No definition available.

+ Details

Name:	gk_Numberofmultiemployerpensionplans
Namespace Prefix:	gk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of multiemployer plans we have received formal demand notice

+ References

No definition available.

+ Details

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Namespace Prefix:	gk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Expenses incurred related to the withdrawal from multi-employer pension plans, including incentives for union participants, and other associated expenses.

+ References

No definition available.

+ Details

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Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 35

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

+ Details

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

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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

- Details

Name:	us-gaap_MultiemployerPlansLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

No definition available.

+ Details

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

Employee Benefit Plans - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Dec. 27, 2014	Mar. 29, 2014	Dec. 28, 2013	Sep. 28, 2013	Dec. 27, 2014 Multiemployer_pension_plans	Dec. 28, 2013
Multiemployer Plans [Line Items]
Employer contribution for pension plan					$ 145
Demand notice aggregate payments of multiemployer plan withdrawal liability			56,000			56,000
Period of payment of withdrawal liability (in years)			20 years
Demand notice multiemployer plan withdrawal liability			35,100			35,100
Aggregate payments of multiemployer pension plan withdrawal liability			34,500			34,500
Discount rate (in percent)			5.25%us-gaap_FairValueInputsDiscountRate
Multi-employer plan withdrawal liability			23,500			23,500
Accretion expense			113us-gaap_AccretionExpense
Pension withdrawal and associated expenses	0	8,167	0	1,687	0	1,687
Payments made to the Central States Fund					$ 1,400	$ 934
Number of remaining other MEPPs					4gk_Numberofmultiemployerpensionplans
Number of MEPPs we have received a formal demand notice					3
Number of MEPPs determined reasonable					2gk_NumberofMEPPsdeterminedreasonable