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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved rate increase (decrease) by regulatory agency.

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Amount of public utility's amended requested rate increase (decrease) with 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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Washington Utilities and Transportation Commission (WUTC) (Details 5) - WUTC - USD ($) $ in Millions	Jul. 20, 2018	Jun. 01, 2018	Mar. 23, 2018	Aug. 31, 2017
Natural gas rate proceeding
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount				$ 5.9
Public utilities, requested rate increase (decrease), percentage				2.70%
Natural gas rate proceeding \| Tax Cuts and Jobs Act
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amended, amount			$ (1.7)
Pipeline replacement cost recovery
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 2.3
Public utilities, requested rate increase (decrease), percentage		1.10%
Subsequent Event \| Natural gas rate proceeding \| Tax Cuts and Jobs Act
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount	$ (2.9)
Public utilities, approved rate increase (decrease), percentage	(1.40%)
Public utilities, approved refund of excess deferred income taxes, amount	$ 2.5
Public utilities, refund interim tax benefits to customers	$ 1.6