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v3.19.1

Background and Basis of Presentation (Details) | 1 Months Ended | 3 Months Ended
--- | --- | ---
Jan. 31, 2017 a | Mar. 31, 2019 mi
Leases |  |
Length of pipeline to supply gas | mi |  | 137
City Of Texas City and State Of Texas (Galveston Bay) | Surface leases |  |
Leases |  |
Term of lease agreement | 36 months |
Area of land leased | a | 994 |

X
- Definition Represents surface area available for lease. + References No definition available. + Details
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Namespace Prefix: | next_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the length of pipeline to supply gas. + References No definition available. + Details
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Namespace Prefix: | next_
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Balance Type: | na
Period Type: | duration

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- 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
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Namespace Prefix: | us-gaap_
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Period Type: | duration

X
- Definition Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980 + Details
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- Details
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- Details
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Namespace Prefix: |
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Period Type: |