Stockholders' equity (deficit) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 320,088	$ 26,553	$ 910,691	$ 55,480
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	320,088	26,553	910,691	55,480
Stock options | Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	70,228	5,975	106,684	12,069
Stock options | General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	199,179	19,818	282,478	41,878
Stock options | Sales and marketing activities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 50,681	$ 760	$ 521,529	$ 1,533