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Stock-Based Compensation (Restricted Stock) (Details) (USD $)
3 Months Ended 0 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Jan. 16, 2015
Mar. 19, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation cost related to awards, weighted average period for recognition 12 months      
Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense 679,770us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
$ 692,682us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
   
Total unrecognized compensation expense 2,715,334us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Chief Executive Officer | Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards granted in period     83,590us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
 
Award vesting period     1 year  
Executive Officer | Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period       1 year
Chief Financial Officer | Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards granted in period       20,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefFinancialOfficerMember
Vice President of Technical Services | Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards granted in period       20,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_TitleOfIndividualAxis
= ngs_VicePresidentofTechnicalServicesMember
Directors | Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards granted in period       21,968us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
Award vesting period       1 year