XML 34 R22.htm IDEA: XBRL DOCUMENT v3.8.0.1

Basis of Presentation and Summary of Significant Accounting Policies Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Contract Assets
Increases due to cash received, excluding amounts recognized as revenue during the period	$ 0
Transferred to receivables from contract assets recognized at the beginning of the period	0
Contract Liabilities
Revenue Recognized that was included in the contract liability balance at the beginning of the year
Increases due to cash received, excluding amounts recognized as revenue during the period

X

- Definition

Contract with Customer, Asset, Increases Due To Cash Received

+ References

No definition available.

+ Details

Name:	ngs_ContractwithCustomerAssetIncreasesDueToCashReceived
Namespace Prefix:	ngs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Contract with Customer, Liability, Increase from Cash Receipts

+ References

No definition available.

+ Details

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

X

- References

No definition available.

+ Details

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

X

- Definition

Amount of decrease in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time from transfer to receivable due to right to consideration becoming unconditional.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130551-203045

+ Details

Name:	us-gaap_ContractWithCustomerAssetReclassifiedToReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130549-203045

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration