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Credit Facility (Details) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013
Line of Credit Facility [Line Items] |  |
Line of credit | $ 0us-gaap_LinesOfCreditCurrent | $ 577,000us-gaap_LinesOfCreditCurrent
Revolving Credit Facility |  |
Line of Credit Facility [Line Items] |  |
Maximum borrowing capacity | 30,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Potential maximum borrowing capacity | 50,000,000ngs_LineOfCreditFacilityPotentialMaximumBorrowingCapacity / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Potential increase in borrowing capacity | 20,000,000ngs_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Borrowing base, component, % of eligible accounts receivable | 80.00%ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleAccountsReceivable / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Borrowing base, component, % of eligible inventory | 50.00%ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleGeneralInventory / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Borrowing base, allowable share of total commitment amount attributable to inventory component | 50.00%ngs_LineOfCreditFacilityCurrentBorrowingCapacityAllowableShareOfTotalCommitmentAmountAttributableToGeneralInventoryComponent / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Borrowing base, component, % of eligible equipment inventory | 75.00%ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleEquipmentInventory / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Borrowing base amount available | 29,600,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Line of credit | 417,000us-gaap_LinesOfCreditCurrent / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Weighted average interest rate | 1.40%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
LIBOR-based Rate | Revolving Credit Facility |  |
Line of Credit Facility [Line Items] |  |
Variable rate, applicable margin | 1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / ngs_ReferenceRateAxis = ngs_LiborBasedRateMember |
CB Floating Rate | Revolving Credit Facility |  |
Line of Credit Facility [Line Items] |  |
Variable rate, applicable margin | 1.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / ngs_ReferenceRateAxis = ngs_CbFloatingRateMember |
Maximum | Revolving Credit Facility |  |
Line of Credit Facility [Line Items] |  |
Maximum leverage ratio allowed | 2.50ngs_LineofCreditFacilityLeverageRatio / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Default trigger, certain defaults of other company indebtedness, amount | 50,000ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Default trigger, rendering of certain judgments, amount | $ 150,000ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Maximum | LIBOR-based Rate | Revolving Credit Facility |  |
Line of Credit Facility [Line Items] |  |
Reference rate, number of allowable LIBOR-based borrowings outstanding | 3ngs_LineOfCreditFacilityReferenceRateNumberOfAllowableBorrowingsOutstanding / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember / ngs_ReferenceRateAxis = ngs_LiborBasedRateMember |
Minimum | Revolving Credit Facility |  |
Line of Credit Facility [Line Items] |  |
Minimum commitment coverage ratio allowed | 2.00ngs_LineofCreditFacilityCommitmentCoverageRatio / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MinimumMember |

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- Definition Line of Credit Facility, Minimum Commitment Coverage Ratio Allowed + References No definition available. + Details
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Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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- Definition Line of Credit Facility, Current Borrowing Capacity, Allowable Share of Total Commitment Amount Attributable to General Inventory Component + References No definition available. + Details
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Namespace Prefix: | ngs_
Data Type: | num:percentItemType
Balance Type: | na
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- Definition Line of Credit Facility, Current Borrowing Capacity, Component, Percentage of Eligible Accounts Receivable + References No definition available. + Details
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Namespace Prefix: | ngs_
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Balance Type: | na
Period Type: | instant

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- Definition Line of Credit Facility, Current Borrowing Capacity, Component, Percentage of Eligible Equipment Inventory + References No definition available. + Details
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Namespace Prefix: | ngs_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Line of Credit Facility, Current Borrowing Capacity, Component, Percentage of Eligible General Inventory + References No definition available. + Details
Name: | ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleGeneralInventory
Namespace Prefix: | ngs_
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Balance Type: | na
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- Definition Line of Credit Facility, Default Trigger, Certain Defaults of Other Company Indebtedness, Amount + References No definition available. + Details
Name: | ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount
Namespace Prefix: | ngs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line of Credit Facility, Default Trigger, Rendering of Certain Judgments, Amount + References No definition available. + Details
Name: | ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount
Namespace Prefix: | ngs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line of Credit Facility, Maximum Leverage Ratio Allowed + References No definition available. + Details
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Namespace Prefix: | ngs_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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- Definition Line of Credit Facility, Potential Increase in Borrowing Capacity + References No definition available. + Details
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Namespace Prefix: | ngs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Line of Credit Facility, Potential Maximum Borrowing Capacity + References No definition available. + Details
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Namespace Prefix: | ngs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line of Credit Facility, Reference Rate, Number of Allowable Borrowings Outstanding (e.g. LIBOR Rate, CB Floating Rate, etc.) + References No definition available. + Details
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Namespace Prefix: | ngs_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The effective interest rate during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Line-of-Credit Arrangement -URI http://asc.fasb.org/extlink&oid=6517033 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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