XML 42 R78.htm IDEA: XBRL DOCUMENT
v3.20.1

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract] |  |  |
401(k) plan, minimum eligibility age | 18 years |  |
401(k) plan, requisite service period | 2 months |  |
401(k) plan, maximum annual contribution per employee, percent | 100.00% |  |
401(k) plan, employer's matching contribution, annual vesting percentage | 20.00% |  |
401(k) plan, employer contribution, ultimate vesting percentage | 100.00% |  |
401(k) plan, employer's matching contribution, vesting term | 6 years |  |
401(k) plan, employer contribution amount | $ 393 | $ 355 | $ 301

X
- Definition Defined Contribution Plan, Eligibility Age, Minimum + References No definition available. + Details
Name: | ngs_DefinedContributionPlanEligibilityAgeMinimum
Namespace Prefix: | ngs_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Contribution Plan, Employer Contribution Amount + References No definition available. + Details
Name: | ngs_DefinedContributionPlanEmployerContributionAmount
Namespace Prefix: | ngs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Defined Contribution Plan, Employer Contribution, Ultimate Vesting Percentage + References No definition available. + Details
Name: | ngs_DefinedContributionPlanEmployerContributionUltimateVestingPercentage
Namespace Prefix: | ngs_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Contribution Plan, Employers Matching Contribution, Vesting Term + References No definition available. + Details
Name: | ngs_DefinedContributionPlanEmployersMatchingContributionVestingTerm
Namespace Prefix: | ngs_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Contribution Plan, Requisite Service Period + References No definition available. + Details
Name: | ngs_DefinedContributionPlanRequisiteServicePeriod
Namespace Prefix: | ngs_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Percentage of employer's matching contributions to a defined contribution plan that vests in a given year. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration