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Gas in Storage (Details) - USD ($) $ in Millions | Mar. 31, 2020 | Dec. 31, 2019
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Gas in Storage [Abstract] |  |
LIFO Inventory Amount | $ 29.9 | $ 0.0

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- Definition Gas in Storage [Abstract] + References No definition available. + Details
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Namespace Prefix: | nix_
Data Type: | xbrli:stringItemType
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- Definition The amount of LIFO (last in first out) inventory present at the reporting date when inventory is also valued using different valuation methods. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6361739&loc=d3e7789-107766 + Details
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Balance Type: | debit
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