XML 57 R46.htm IDEA: XBRL DOCUMENT
v3.20.2

Stock-Based and Other Long-Term Incentive Compensation (Summary of Unvested Stock Options) (Details) - USD ($) | 6 Months Ended
--- | ---
Jun. 30, 2020 | Jun. 30, 2019
Shares |  |
Unvested, beginning of period (in shares) | 10,433 |
Granted (in shares) | 5,000 |
Vested (in shares) | (10,433) |
Canceled/Forfeited (in shares) | 0 |
Unvested, end of period (in shares) | 5,000 |
Weighted AverageGrant Date Fair Value Per Share |  |
Unvested, weighted average grant date fair value, beginning of period (in USD per share) | $ 11.93 |
Granted, weighted average grant date fair value (in USD per share) | 2.07 |
Vested, weighted average grant date fair value (in USD per share) | 11.93 |
Canceled/Forfeited, weighted average grant date fair value (in USD per share) | 0 |
Unvested, weighted average grant date fair value, end of period (in USD per share) | $ 2.07 |
Stock Options |  |
Weighted AverageGrant Date Fair Value Per Share |  |
Unrecognized compensation cost related to unvested options | $ 8,000 |
Share-based compensation expense | $ 18,000 | $ 61,000

X
- Definition Employee Service Share-based Compensation, Nonvested Awards, Stock Options, Outstanding [Roll Forward] + References No definition available. + Details
Name: | ngs_EmployeeServiceShareBasedCompensationNonvestedAwardsStockOptionsOutstandingRollForward
Namespace Prefix: | ngs_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Employee Service Share-based Compensation, Nonvested Awards, Stock Options, Weighted Average Grant Date Fair Value [Roll Forward] + References No definition available. + Details
Name: | ngs_EmployeeServiceShareBasedCompensationNonvestedAwardsStockOptionsWeightedAverageGrantDateFairValueRollForward
Namespace Prefix: | ngs_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | ngs_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsCanceledOrForfeitedNumberOfShares
Namespace Prefix: | ngs_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | ngs_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsCanceledOrForfeitedWeightedAverageGrantDateFairValue
Namespace Prefix: | ngs_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of cost to be recognized for option under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of non-vested options outstanding. + References No definition available. + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Weighted average grant-date fair value of non-vested options outstanding. + References No definition available. + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of options vested. + References No definition available. + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average grant-date fair value of options vested. + References No definition available. + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |