Receivables (Rollforward of Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Allowance for Doubtful Accounts [Roll Forward]
Balance as of beginning of period	$ 1,514	$ 1,542
Current period provision	146	479
Direct write-offs charged against the allowance	(127)	(507)
Balance as of end of period	$ 1,533	$ 1,514