Significant Accounting Policies - Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	7,518,390	7,028,256
Outstanding common stock options
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	6,265,333	6,544,738
Outstanding warrants
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	756,647	34,647
RSUs
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	478,087	414,018
Employee Stock Purchase Plan
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	18,323	34,853