Trade accounts receivable - net (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance		$ 335	$ 244	$ 227
Provision for Doubtful Accounts		21	99	31
Deductions and Other	[1]	9	(8)	(14)
Ending Balance		$ 365	$ 335	$ 244

[1] 2016 includes a reclassification adjustment not affecting operations