Net Loss per Share - Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	3,814,552	8,791,372	8,840,359
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	3,059,690	2,791,754	2,845,226
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	722,646
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	32,216	446,593	442,108
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