Net Income (Loss) per Share - antidilutive (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	6,880,767	6,290,870	5,541,050
Outstanding common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	6,447,594	5,686,815	5,096,674
Outstanding warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	34,647	34,647	34,647
PRSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	0	213,758	245,396
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	394,132	351,414	161,439
Employee Stock Purchase Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	4,394	4,236	2,894