Revenue Refunded To Customers As A Result Of The TCJA Tax Benefits

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Significant Judgments and Estimates [Abstract]

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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.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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The amount of regulated other operating revenues recognized during the period.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Business Description and Summary of Significant Accounting Policies: Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 297,577
Regulated Operating Revenue, Other									503
Revenue	$ 75,522	$ 78,067	$ 70,676	$ 73,815	$ 74,648	$ 73,938	$ 66,053	$ 73,794	298,080	$ 288,433	$ 267,632
Significant Judgments and Estimates [Abstract]
Revenue Refunded To Customers As A Result Of The TCJA Tax Benefits									7,600
Regulatory Liabilities	163,216				148,855				163,216	148,855
Revenue Subject to Refund
Significant Judgments and Estimates [Abstract]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount									10,000
Revenue Refunded To Customers As A Result Of The TCJA Tax Benefits									900
Regulatory Liabilities	$ 2,523				$ 0				2,523	$ 0
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									297,577
Regulated Utility Retail
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									197,184
Regulated Utility Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									33,687
Regulated Utility Market Off-System Sales
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									17,691
Regulated Utility Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 49,015