Employee Benefit Plans: Plan Contributions (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 1,800
Defined Benefit Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Pension Plan - Employer contributions	1,795	$ 4,000
Non-pension Defined Benefit Postretirement Healthcare Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Pension Plan - Employer contributions	268	248
Defined Benefit Plans - Other, Employer Contributions	388	348
Supplemental Non-qualified Defined Benefit Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Pension Plan - Employer contributions	238	246
Defined Benefit Plans - Other, Employer Contributions	238	246
Company Retirement Contribution
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plans, Contributions by Employer	876	861
Matching Contributions
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plans, Contributions by Employer	$ 1,272	$ 1,306

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

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Amount of cost for defined contribution plan.

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Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

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