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Summary of Significant Accounting Policies - Additional Information (Details) (USD $)
 12 Months Ended 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jun. 28, 2013
Mar. 29, 2013
Significant Accounting Policies [Line Items]          
Earnings from equity investment $ 2,700,000us-gaap_IncomeLossFromEquityMethodInvestments $ 1,469,000us-gaap_IncomeLossFromEquityMethodInvestments $ 556,000us-gaap_IncomeLossFromEquityMethodInvestments    
Net investment $ 8,000,000us-gaap_EquityMethodInvestments $ 5,700,000us-gaap_EquityMethodInvestments      
Laser Quantum          
Significant Accounting Policies [Line Items]          
Equity method investment ownership percentage 41.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gsig_LaserQuantumLtdMember		 41.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gsig_LaserQuantumLtdMember		      
Equity method investment ownership percentage in Laser Quantum       41.00%us-gaap_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipAfterAllTransactions
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gsig_LaserQuantumLtdMember		 25.00%us-gaap_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipAfterAllTransactions
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gsig_LaserQuantumLtdMember
Maximum          
Significant Accounting Policies [Line Items]          
Cash equivalents original maturity period 3 months        
Equity method investment ownership percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		        
Payment terms 180 days        
Maximum | Laser Products          
Significant Accounting Policies [Line Items]          
Standard warranty period 24 months        
Maximum | Precision Motion          
Significant Accounting Policies [Line Items]          
Standard warranty period 24 months        
Maximum | Medical Technologies          
Significant Accounting Policies [Line Items]          
Standard warranty period 60 months        
Maximum | Buildings and improvements          
Significant Accounting Policies [Line Items]          
Property, plant and equipment, estimated useful lives 30 years        
Maximum | Machinery and Equipment          
Significant Accounting Policies [Line Items]          
Property, plant and equipment, estimated useful lives 10 years        
Minimum          
Significant Accounting Policies [Line Items]          
Equity method investment ownership percentage 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		        
Minimum | Laser Products          
Significant Accounting Policies [Line Items]          
Standard warranty period 12 months        
Minimum | Precision Motion          
Significant Accounting Policies [Line Items]          
Standard warranty period 12 months        
Minimum | Medical Technologies          
Significant Accounting Policies [Line Items]          
Standard warranty period 12 months        
Minimum | Buildings and improvements          
Significant Accounting Policies [Line Items]          
Property, plant and equipment, estimated useful lives 3 years        
Minimum | Machinery and Equipment          
Significant Accounting Policies [Line Items]          
Property, plant and equipment, estimated useful lives 1 year