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

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

No definition available.

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

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

No definition available.

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

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

No definition available.

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

Line of Credit Facility, Default Trigger, Certain Defaults of Other Company Indebtedness, Amount

No definition available.

Name:	ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount
Namespace Prefix:	ngs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line of Credit Facility, Default Trigger, Rendering of Certain Judgments, Amount

No definition available.

Name:	ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount
Namespace Prefix:	ngs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line of Credit Facility, Potential Increase in Borrowing Capacity

No definition available.

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

Line of Credit Facility, Potential Maximum Borrowing Capacity

No definition available.

Name:	ngs_LineOfCreditFacilityPotentialMaximumBorrowingCapacity
Namespace Prefix:	ngs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line of Credit Facility, Reference Rate, Number of Allowable Borrowings Outstanding (e.g. LIBOR Rate, CB Floating Rate, etc.)

No definition available.

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

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

Line of Credit Facility, Maximum Leverage Ratio Allowed

No definition available.

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

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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.

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

The effective interest rate during the reporting period.

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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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

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.

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

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.

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
-Topic 470
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=28361426&loc=d3e1314-112600

Reference 3: 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

Reference 4: 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

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

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

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

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

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