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Balance Sheets (Parenthetical) (USD $)
In Thousands, except Share data, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Current Assets:    
Allowance for doubtful accounts $ 507us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 436us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Allowance for inventory obsolescence 225us-gaap_InventoryValuationReserves 128us-gaap_InventoryValuationReserves
Assets, Noncurrent [Abstract]    
Accumulated depreciation, rental equipment 106,179ngs_AccumulatedDepreciationRentalEquipment 86,533ngs_AccumulatedDepreciationRentalEquipment
Accumulated depreciation, property and equipment 10,830us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment 9,692us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
Accumulated amortization, intangibles $ 1,257ngs_IntangibleAssetsAccumulatedAmortization $ 1,132ngs_IntangibleAssetsAccumulatedAmortization
Stockholders' Equity Attributable to Parent [Abstract]    
Preferred stock, shares authorized 5,000,000us-gaap_PreferredStockSharesAuthorized 5,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued 0us-gaap_PreferredStockSharesIssued 0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding 0us-gaap_PreferredStockSharesOutstanding 0us-gaap_PreferredStockSharesOutstanding
Common stock, par value $ 0.01us-gaap_CommonStockParOrStatedValuePerShare $ 0.01us-gaap_CommonStockParOrStatedValuePerShare
Common stock, shares authorized 30,000,000us-gaap_CommonStockSharesAuthorized 30,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued 12,466,000us-gaap_CommonStockSharesIssued 12,366,000us-gaap_CommonStockSharesIssued
Common stock, shares outstanding 12,466,000us-gaap_CommonStockSharesOutstanding 12,366,000us-gaap_CommonStockSharesOutstanding