Stockholders' equity - Company Recognized Stock Compensation Expense (Details) - USD ($)	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]
Allocated share-based compensation expense	$ 206,651	$ 267,592	$ 658,731	$ 722,304
Cost of Services [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	(2,807)	2,306	924	6,274
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	56,961	61,097	187,512	171,652
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	141,974	187,357	434,314	500,252
Sales and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 10,523	$ 16,832	$ 35,981	$ 44,126