Trade accounts receivable - net - Reserves for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Trade accounts receivable - net
Beginning Balance	$ 1,178	$ 722
Net additions charged to Operations	(76)	479
Deductions and Other	(392)	(23)
Ending Balance	$ 710	$ 1,178