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Employee Benefit Plans: Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Hedge Funds | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	15 days
Hedge Funds | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	60 days
Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 458,387	$ 473,721	$ 434,284
Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	458,387	473,721
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	415,490	441,966
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	42,897	31,755
Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	7,972	8,165
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	7,972	8,165
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	7,972	8,165
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	415,490	441,966
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	0	0
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	6,009	16,810
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	6,009	16,810
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0	0
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	6,009	16,810
Common Collective Trust, Cash And Cash Equivalents | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Common Collective Trust, Equity Fund | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	70,262	100,311
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	70,262	100,311
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0	0
Common Collective Trust, Equity Fund | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Common Collective Trust, Equity Fund | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	70,262	100,311
Common Collective Trust, Equity Fund | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Common Collective Trust, Fixed Income Fund | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	339,219	324,845
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	339,219	324,845
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	0	0
Common Collective Trust, Fixed Income Fund | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Common Collective Trust, Fixed Income Fund | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	339,219	324,845
Common Collective Trust, Fixed Income Fund | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Real Estate Funds | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	30,407	14,301
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	0	0
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	30,407	14,301
Real Estate Funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Real Estate Funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Real Estate Funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 0	0
Hedge Funds | Minimum
Percentage Of Monthly Redemption	10.00%
Hedge Funds | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	$ 12,490	17,454
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	0	0
Defined Benefit Plan, Alternative Investments, Fair Value Of Plan Assets	12,490	17,454
Hedge Funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Hedge Funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Hedge Funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan, Plan Assets, Amount	0	0
Cash | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	7,972	8,165
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments	7,972	8,165
Cash | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	7,972	8,165
Cash | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	0	0
Cash | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Postretirement Health Coverage
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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