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Components of Gas Inventory (Detail) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
--- | --- | --- | ---
Public Utilities, Inventory [Line Items] |  |  |
Weighted average cost inventory amount | $ 0.9 | $ 0.6 | $ 0.7
Liquefied Natural Gas & Other |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Weighted average cost inventory amount | 0.1 | 0.1 | 0.1
Natural Gas |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Weighted average cost inventory amount | 0.4 | 0.4 | 0.4
Propane |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Weighted average cost inventory amount | $ 0.4 | $ 0.1 | $ 0.2

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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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- Definition The amount of weighted average cost inventory present at the reporting date when inventory is 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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