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Other Long-term Liabilities (Details) (USD $)
 3 Months Ended 0 Months Ended
Mar. 31, 2013
Jul. 30, 2008
Dec. 31, 2012
Dec. 31, 2014
Dec. 31, 2013
Other Long-term Liabilities          
Deferred revenue, noncurrent, related to certain staffing requirements     $ 275,000us-gaap_DeferredRevenueNoncurrent    
Payments to settle deferred revenue liability 52,000ngs_PaymentsToSettleDeferredRevenueLiability        
Gain (loss) on settlement of deferred revenue liability 223,000ngs_GainLossOnSettlementOfDeferredRevenueLiability        
Paint and Coatings          
Other Long-term Liabilities          
Long-term purchase commitment, amount   4,800,000us-gaap_LongTermPurchaseCommitmentAmount
/ us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis
= us-gaap_InventoriesMember		      
Cash received from supplier as discount toward future purchases   300,000ngs_LongTermPurchaseCommitmentCashReceivedAsDiscountTowardFuturePurchases
/ us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis
= us-gaap_InventoriesMember		      
Liability related to deferred discount   $ 300,000ngs_LongTermPurchaseCommitmentLiabilityRelatedToDeferredDiscount
/ us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis
= us-gaap_InventoriesMember		   $ 155,000ngs_LongTermPurchaseCommitmentLiabilityRelatedToDeferredDiscount
/ us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis
= us-gaap_InventoriesMember		 $ 197,000ngs_LongTermPurchaseCommitmentLiabilityRelatedToDeferredDiscount
/ us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis
= us-gaap_InventoriesMember