Credit Facility (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Line of credit, non-current portion	$ 417,000us-gaap_LongTermLineOfCredit	$ 417,000us-gaap_LongTermLineOfCredit
Revolving Credit Facility
Line of Credit Facility [Line Items]
Borrowing base amount available	29,600,000	30,000,000
Potential increase in borrowing capacity	20,000,000
Maximum borrowing capacity	50,000,000
Borrowing base, component, % of eligible accounts receivable	80.00%
Borrowing base, component, % of eligible inventory	50.00%
Borrowing base, allowable share of total commitment amount attributable to inventory component	50.00%
Borrowing base, component, % of eligible equipment inventory	75.00%
Weighted average interest rate	1.42%
Default trigger, certain defaults of other company indebtedness, amount	50,000
Default trigger, rendering of certain judgments, amount	150,000
Line of credit, non-current portion	$ 417,000	$ 417,000
LIBOR Rate \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Reference rate, number of allowable LIBOR-based borrowings outstanding	3
Variable rate, applicable margin	1.50%
CB Floating Rate \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Variable rate, applicable margin	1.50%
Minimum \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Minimum commitment coverage ratio allowed	2.00
Maximum \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum leverage ratio allowed	2.50

Line of Credit Facility, Minimum Commitment Coverage Ratio Allowed

No definition available.

Name:	ngs_LineofCreditFacilityCommitmentCoverageRatio
Namespace Prefix:	ngs_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Current Borrowing Capacity, Allowable Share of Total Commitment Amount Attributable to General Inventory Component

+ References

No definition available.

+ Details

Name:	ngs_LineOfCreditFacilityCurrentBorrowingCapacityAllowableShareOfTotalCommitmentAmountAttributableToGeneralInventoryComponent
Namespace Prefix:	ngs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Current Borrowing Capacity, Component, Percentage of Eligible Accounts Receivable

+ References

No definition available.

+ Details

Name:	ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleAccountsReceivable
Namespace Prefix:	ngs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Current Borrowing Capacity, Component, Percentage of Eligible Equipment Inventory

+ References

No definition available.

+ Details

Name:	ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleEquipmentInventory
Namespace Prefix:	ngs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

- 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

- Definition

Line of Credit Facility, Maximum Leverage Ratio Allowed

+ References

No definition available.

+ Details

Name:	ngs_LineofCreditFacilityLeverageRatio
Namespace Prefix:	ngs_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Potential Increase in Borrowing Capacity

+ References

No definition available.

+ Details

Name:	ngs_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity
Namespace Prefix:	ngs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

Name:	ngs_LineOfCreditFacilityReferenceRateNumberOfAllowableBorrowingsOutstanding
Namespace Prefix:	ngs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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

- 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

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the noncurrent 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 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: 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

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 45

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=28361426&loc=d3e1314-112600

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 45

-Paragraph 14

-URI http://asc.fasb.org/extlink&oid=28361426&loc=d3e1336-112600

+ Details

Name:	us-gaap_LongTermLineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=ngs_CbFloatingRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: