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Debt (Details) (USD $)
In Thousands, unless otherwise specified
Apr. 03, 2015
Dec. 31, 2014
Debt Instrument [Line Items]    
Senior Credit Facilities $ 123,125us-gaap_DebtLongtermAndShorttermCombinedAmount $ 115,000us-gaap_DebtLongtermAndShorttermCombinedAmount
Senior Credit Facilities 115,625us-gaap_LongTermDebtNoncurrent 107,500us-gaap_LongTermDebtNoncurrent
Term Loans    
Debt Instrument [Line Items]    
Senior Credit Facilities 33,125us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_CreditFacilityAxis
= gsig_TermLoanMember		 35,000us-gaap_DebtLongtermAndShorttermCombinedAmount
/ us-gaap_CreditFacilityAxis
= gsig_TermLoanMember
Revolving Credit Facility    
Debt Instrument [Line Items]    
Senior Credit Facilities $ 90,000us-gaap_LongTermDebtNoncurrent
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember		 $ 80,000us-gaap_LongTermDebtNoncurrent
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember