Rate and Regulatory Matters - Summary of interim rate information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2016
Public Utilities, General Disclosures [Line Items]
Interim Revenue Increase (subject to refund)	$ 3,818	$ 6,875
2016 Test Year Allocation
Public Utilities, General Disclosures [Line Items]
Revenue Increase Requested		$ 19,296
Increase Percentage Requested		9.80%
Jurisdictional Rate Base		$ 483,000
Interim Revenue Increase (subject to refund)		$ 16,816

Amount of public utility's jurisdictional rate base investment on which a return is requested.

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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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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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