Employee Benefit Plans: Change in Accounting Principle (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Other income (expense), net	$ (1,863)	$ 263	$ 490	$ (526)
Income tax (expense)	(4,831)	(2,307)	(20,833)	(19,570)
Net income available for common stock	$ 20,966	$ 14,583	114,140	$ 118,391
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