Selected Balance Sheet Information: Changes to Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss, Current	$ 8,609	$ 8,609	$ 3,159	$ 2,444	$ 3,209
Additions Charged to Costs and Expenses		8,471	5,637
Recoveries and Other Additions		3,720	2,742
Write-offs and Other Deductions		(6,026)	$ (8,429)
Adjustment Related to COVID-19
Additions Charged to Costs and Expenses	$ 1,700	$ 3,700