XML 49 R33.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Rental Activity (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Property Subject to or Available for Operating Lease [Line Items] |  |  |
Depreciation | $ 21,147 | $ 21,641 | $ 22,605
2018 | 6,494 |  |
2019 | 976 |  |
2020 | 543 |  |
2021 | 542 |  |
2022 | 542 |  |
Total | $ 9,097 |  |
Minimum |  |  |
Property Subject to or Available for Operating Lease [Line Items] |  |  |
Rental arrangements, original term | 6 months |  |
Maximum |  |  |
Property Subject to or Available for Operating Lease [Line Items] |  |  |
Rental arrangements, original term | 24 months |  |
Rental Equipment |  |  |
Property Subject to or Available for Operating Lease [Line Items] |  |  |
Depreciation | $ 20,000 | $ 20,200 | $ 21,000

X
- Definition Operating Leases of Lessor, Original Term + References No definition available. + Details
Name: | ngs_OperatingLeasesOfLessorOriginalTerm
Namespace Prefix: | ngs_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
Name: | us-gaap_Depreciation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Future minimum rental payments in aggregate as of the balance sheet date under operating leases. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Future rental payments receivable within one year of the balance sheet date under an operating lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Future rental payments receivable within the fifth year from the balance sheet date under an operating lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInFiveYears
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Future rental payments receivable within the fourth year from the balance sheet date under an operating lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInFourYears
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Future rental payments receivable within the third year from the balance sheet date under an operating lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInThreeYears
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Future rental payments receivable within the second year from the balance sheet date under an operating lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInTwoYears
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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_PropertySubjectToOrAvailableForOperatingLeaseLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_EquipmentLeasedToOtherPartyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |