Significant Accounting Policies - Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	7,028,256	6,320,112
Outstanding common stock options
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	6,544,738	5,693,156
Outstanding warrants
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	34,647	34,647
PRSUs
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share		216,008
RSUs
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	414,018	352,949
Employee Stock Purchase Plan
Common stock equivalents
Antidilutive securities excluded from computation of earnings per share	34,853	23,352