Business Description and Summary of Significant Accounting Policies: Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	$ 75,732	$ 78,703
Regulatory Assets, Current	(19,052)	(18,993)
Regulatory assets, non-current	56,680	59,710
Regulatory Liabilities	163,216	148,855
Regulatory Liability, Current	(2,574)	(842)
Regulatory liabilities, non-current	160,642	148,013
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)		103,000
Cost of removal for utility plant
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Liabilities	52,366	44,056
Employee benefit plans
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Liabilities	7,518	6,808
Deferred Income Tax Charges
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Liabilities	100,276	97,101
Tax Cuts and Jobs Act of 2017, Provisional Income Tax Expense (Benefit)	100,000
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)		97,000
Revenue Subject to Refund
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Liabilities	2,523	0
Other regulatory liabilities
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Liabilities	533	890
Unamortized loss on reacquired debt
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	1,259	1,534
Allowance for Funds Used During Construction
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	5,020	5,095
Employee benefit plans
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	19,868	19,465
Deferred energy costs
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	20,334	19,602
Flow through accounting
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	8,749	7,579
Decommissioning costs
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	8,196	10,252
Vegetation Management
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	10,366	12,669
Other Regulatory Assets
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory Assets	$ 1,940	$ 2,507