Net Income (Loss) per Share - Anti-dilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
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	3,954,350	3,979,936
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	2,809,641	3,219,862
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	1,144,709	727,858
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