Principles Of Preparation (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020
Accounts Receivable, after Allowance for Credit Loss [Abstract]
Balance at beginning of period	$ 1,900	$ 2,070	$ 1,514
Additions:
Increase to provision	676	217	2,800
Recovery of previous write-offs	340	342
Uncollectible receivables written off	(1,138)	(1,115)
Balance at end of period	$ 1,778	$ 1,514	$ 1,778