XML 92 R62.htm IDEA: XBRL DOCUMENT
v3.20.1

Income Taxes Income Taxes (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2019
Income Tax Disclosure [Abstract] |  |
Tax Cuts and Jobs Act, change in tax rate, income tax expense (benefit) |  | $ (18,400)
Net operating loss carryforward |  | 6,700
Income Tax Contingency [Line Items] |  |
Tax Cuts and Jobs Act, change in tax rate, income tax expense (benefit) |  | (18,400)
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions | $ 547 |
Income tax penalties and interest accrued | $ 55 |
Net operating loss carryforward |  | 6,700
Tax Year 2017 |  |
Income Tax Contingency [Line Items] |  |
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions |  | 168
Tax Year 2016 |  |
Income Tax Contingency [Line Items] |  |
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions |  | 149
Tax Year 2015 |  |
Income Tax Contingency [Line Items] |  |
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions |  | $ 230

X
- Definition Tax Cuts and Jobs Act, Change in Tax Rate, Income Tax Expense (Benefit) + References No definition available. + Details
Name: | ngs_TaxCutsandJobsActChangeinTaxRateIncomeTaxExpenseBenefit
Namespace Prefix: | ngs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition 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. + References No definition available. + Details
Name: | us-gaap_IncomeTaxContingencyLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
Name: | us-gaap_OperatingLossCarryforwards
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_TaxPeriodAxis=us-gaap_TaxYear2017Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TaxPeriodAxis=us-gaap_TaxYear2016Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TaxPeriodAxis=us-gaap_TaxYear2015Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |