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Montana Public Service Commission (MTPSC) (Details 6) - MTPSC [Member] - Natural gas rate proceeding [Member] $ in Millions	Sep. 25, 2017 USD ($)
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 2.8
Public utilities, requested rate increase (decrease), percentage	4.10%
Public utilities, interim rate increase (decrease), amount	$ 1.6
Public utilities, interim rate increase (decrease), percentage	2.30%

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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Percentage of public utility's requested rate increase (decrease) with regulatory agency.

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