Employee Benefit Plans: Change in Accounting Principle (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Other income (expense), net	$ (1,193)	$ 580	$ (703)	$ 55
Income tax (expense)	(4,651)	(2,508)	(25,484)	(22,078)
Net income available for common stock	$ 36,283	$ 11,740	150,423	$ 130,131
Cumulative Effect, Period of Adoption, Adjustment
Defined Benefit Plan Disclosure [Line Items]
Other income (expense), net			600
Income tax (expense)			200
Net income available for common stock			$ 400