Receivables (Rollforward of Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts [Roll Forward]
Balance as of beginning of period	$ 1,542	$ 2,644
Allowance for Loan and Lease Losses, Adjustments, Other	461	550
Direct write-offs charged against the allowance	(362)	(1,652)
Balance as of end of period	$ 1,641	$ 1,542