Trade accounts receivable - net - Reserves for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Trade accounts receivable - net
Beginning Balance	$ 710	$ 1,178
Allowance for doubtful accounts	880	(76)
Deductions and Other	7	(392)
Ending Balance	$ 1,597	$ 710