Net Income (Loss) Per Common Share (Anti-Dilutive Common Share Equivalents) (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded (in shares)	6,747,782	5,174,846	5,591,794	5,351,219
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded (in shares)	4,176,551	4,722,904	3,958,602	4,728,587
Warrants to purchase common stock | Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded (in shares)	0	22,000	0	22,000
RSUs and PRSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded (in shares)	2,361,583	429,942	1,633,192	600,632
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded (in shares)	209,648	0	0	0