Net Loss Per Common Share (Anti-Dilutive Common Share Equivalents) (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]
Anti-dilutive common share equivalents (in shares)	15,580,272	12,874,565	10,769,679
Warrants to purchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	1,985,846	2,206,496
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	11,426,296	10,711,321	10,371,469
Common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	2,007,846
Common stock | Warrants to purchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	22,000	309,792	309,792
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	3,888,768	1,853,452	88,418
Employee Stock Purchase Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	243,208	0	0
Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Price of shares entitled to purchase (in dollars per share)	$ 10.70