Stockholders' equity (deficit) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 261,540	$ 24,977	$ 1,172,231	$ 80,457
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	59,688	1,528	161,819	3,903
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	156,236	22,460	443,267	74,032
Sales and marketing activities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 45,616	$ 989	$ 567,145	$ 2,522