Receivables (Rollforward of Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Allowance for Doubtful Accounts [Roll Forward]
Balance as of beginning of period	$ 1,514	$ 1,542
Current period provision	32	479
Direct write-offs charged against the allowance	(1,091)	(507)
Balance as of end of period	$ 455	$ 1,514