Stock Option Plan - Stock-based compensation (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 139	$ 89	$ 470	$ 253
Cost of Revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1	1	1	1
Engineering and Product Development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	9	12	26	36
Sales and Marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	23	24	74	70
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 106	$ 52	$ 369	$ 146