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Deferred Compensation Plans (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) shares	Mar. 31, 2015 USD ($)
Postemployment Benefits [Abstract]
Participant's maximum compensation deferral percentage	90.00%
Company owned life insurance	$ 51
Gain on company owned life insurance	3	$ 0
Deferred compensation obligation	$ 51
Deferred restricted stock shares | shares	0

X

- Definition

Deferred Compensation Arrangement with Individual, Deferred Restricted Stock

+ References

No definition available.

+ Details

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X

- Definition

Deferred Compensation Arrangement with Individual, Maximum Annual Contributions Per Employee, Percent

+ References

No definition available.

+ Details

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Namespace Prefix:	ngs_
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Balance Type:	na
Period Type:	duration

X

- Definition

The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

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X

- Definition

This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

+ 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 210.5-02.12)
-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 325
-SubTopic 30
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6384206&loc=d3e41899-111602

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Balance Type:	debit
Period Type:	instant

X

- Definition

The change in cash surrender or contract value during the period which adjusted the amount of premiums paid in determining the expense or income recognized under the contract for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 30
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6384439&loc=d3e42048-111605

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- References

No definition available.

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