3. Revenue (Details 2) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Contract Assets
Revenue recognized that was included in the contract liability balance at the beginning of the period	$ 0	$ 0
Increase due to cash received, excluding amounts recognized as revenue during the period	0	0
Transferred to receivables from contract assets recognized at the beginning of the period	(3)	(2)
Increase due to additional unamortized discounts	9	11
Contract Liabilities
Revenue recognized that was included in the contract liability balance at the beginning of the period	(760)	(837)
Increase due to cash received, excluding amounts recognized as revenue during the period	876	912
Transferred to receivables from contract assets recognized at the beginning of the period	0	0
Increase due to additional unamortized discounts	$ 0	$ 0