Net loss per share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Series A preferred stock
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	487,494	487,494	487,494	487,494
Series B preferred stock
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	1,297,100	1,297,100	1,297,100	1,297,100
Series B-1 preferred stock
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	2,275,733	2,275,733	2,275,733	2,275,733
Series C preferred stock
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	4,803,492	3,022,306	4,803,492	3,022,306
Warrants | Series C Redeemable Convertible Preferred Stock Warrants
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	819,650	25,000	819,650	25,000
Warrants | Common Stock Warrant
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	337,133	337,133	337,133	337,133
Employee stock options
Net loss per share disclosures
Potentially dilutive shares not included in the calculation of diluted EPS (as converted if related to warrants or redeemable convertible preferred stock)	776,910	404,175	776,910	404,175