Net Loss per Share - Anti-dilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Securities excluded from the calculation of diluted net loss per share attributable to common stockholders
Amount of antidilutive securities excluded from computation of earnings per share	3,688,124	8,491,614	3,688,124	8,491,614
Employee stock options
Securities excluded from the calculation of diluted net loss per share attributable to common stockholders
Amount of antidilutive securities excluded from computation of earnings per share	2,957,302	2,724,783	2,957,302	2,724,783
Restricted stock
Securities excluded from the calculation of diluted net loss per share attributable to common stockholders
Amount of antidilutive securities excluded from computation of earnings per share	730,822		730,822
Common stock warrants
Securities excluded from the calculation of diluted net loss per share attributable to common stockholders
Amount of antidilutive securities excluded from computation of earnings per share		213,806		213,806
Preferred stock warrants
Securities excluded from the calculation of diluted net loss per share attributable to common stockholders
Amount of antidilutive securities excluded from computation of earnings per share		463,589		463,589
Redeemable convertible preferred stock
Securities excluded from the calculation of diluted net loss per share attributable to common stockholders
Amount of antidilutive securities excluded from computation of earnings per share		5,089,436		5,089,436