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Long-Term Debt - Additional Information (Detail) (USD $)
9 Months Ended 0 Months Ended 3 Months Ended
Mar. 28, 2015
Apr. 15, 2020
Mar. 07, 2017
Jun. 27, 2015
Jun. 28, 2014
Apr. 15, 2015
Line of Credit Facility [Line Items]            
Borrowings under $250M revolver $ 25,900,000us-gaap_LineOfCredit       $ 65,925,000us-gaap_LineOfCredit  
Unsecured private placement notes            
Line of Credit Facility [Line Items]            
Long-term debt maturities Jun. 30, 2015          
Outstanding balance, notes 75,000,000us-gaap_LongTermNotesPayable
/ us-gaap_LongtermDebtTypeAxis
= gk_UnsecuredPrivatePlacementNotesMember
         
Effective interest rate (in percent) 0.86%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= gk_UnsecuredPrivatePlacementNotesMember
         
Debt Instrument, description of variable rate basis The notes bear interest at 0.60% over LIBOR          
Debt instrument, frequency of periodic payment The notes do not require principal payments until maturity          
Unsecured debt            
Line of Credit Facility [Line Items]            
Long-term debt, notes 100,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
         
Outstanding balance, notes 100,000,000us-gaap_LongTermNotesPayable
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
         
Effective interest rate (in percent) 3.81%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
         
Unsecured revolving credit facility            
Line of Credit Facility [Line Items]            
Line of Credit Facility, Refinanced Borrowings 250,000,000gk_LineofCreditFacilityRefinancedBorrowings
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
         
Borrowings under $250M revolver 25,900,000us-gaap_LineOfCredit
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
         
Letters of credit outstanding 636,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
         
Fee payment on unused credit balances, percentage 0.20%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
         
Effective interest rate (in percent) 1.56%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
         
Minimum Net Worth Required for Compliance 358,999,000us-gaap_MinimumNetWorthRequiredForCompliance
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
         
Line of credit facility, interest rate description Borrowings in U.S. dollars under this credit facility generally bear interest at the adjusted London Interbank Offered Rate ("LIBOR") for specified interest periods plus a margin, which can range from 1.00% to 2.00%, depending on our consolidated leverage ratio.          
Secured revolving credit facility            
Line of Credit Facility [Line Items]            
Line of credit facility, maximum borrowing capacity 50,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Interest rate spread on notes (in percent) 0.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Interest rate on letters of credit outstanding 0.80%gk_InterestRateonLettersofCreditOutstanding
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Borrowings under $250M revolver 28,100,000us-gaap_LineOfCredit
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Letters of credit outstanding 21,900,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Fee payment on unused credit balances, percentage 0.26%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Effective interest rate (in percent) 0.92%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_CreditFacilityAxis
= gk_SecuredRevolvingCreditFacilityMember
         
Line of credit facility, interest rate description We pay interest at a rate per annum equal to a margin of 0.75%, plus LIBOR.          
Minimum | Unsecured revolving credit facility            
Line of Credit Facility [Line Items]            
Interest rate spread on notes (in percent) 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
         
Maximum | Unsecured revolving credit facility            
Line of Credit Facility [Line Items]            
Interest rate spread on notes (in percent) 2.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
         
Unsecured senior notes 1 | Unsecured debt            
Line of Credit Facility [Line Items]            
Long-term debt, notes 50,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ gk_UnsecuredSeniorNotesAxis
= gk_UnsecuredSeniorNotes1Member
         
Debt instrument, interest rate, stated percentage 3.73%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ gk_UnsecuredSeniorNotesAxis
= gk_UnsecuredSeniorNotes1Member
         
Unsecured senior notes 2 | Unsecured debt            
Line of Credit Facility [Line Items]            
Long-term debt, notes 50,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ gk_UnsecuredSeniorNotesAxis
= gk_UnsecuredSeniorNotes2Member
         
Debt instrument, interest rate, stated percentage 3.88%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember
/ gk_UnsecuredSeniorNotesAxis
= gk_UnsecuredSeniorNotes2Member
         
London Interbank Offered Rate (LIBOR) | Unsecured private placement notes            
Line of Credit Facility [Line Items]            
Interest rate spread on notes (in percent) 0.60%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_LongtermDebtTypeAxis
= gk_UnsecuredPrivatePlacementNotesMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
         
Scenario, forecast | Unsecured revolving credit facility            
Line of Credit Facility [Line Items]            
Debt facility expiration date   Apr. 15, 2020 Mar. 07, 2017      
Borrowings under $250M revolver           $ 30,000,000us-gaap_LineOfCredit
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
Effective interest rate (in percent)           1.44%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
Scenario, forecast | London Interbank Offered Rate (LIBOR) | Minimum | Unsecured revolving credit facility            
Line of Credit Facility [Line Items]            
Interest rate spread on notes (in percent)       1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
   
Scenario, forecast | London Interbank Offered Rate (LIBOR) | Maximum | Unsecured revolving credit facility            
Line of Credit Facility [Line Items]            
Interest rate spread on notes (in percent)       1.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember