Net Loss Per Common Share (Anti-Dilutive Common Share Equivalents) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	13,617,265	13,809,561
Warrants to purchase common stock
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)	10,056,752	10,714,645
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	2,007,846
Warrants to purchase common stock | Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	22,000	22,000
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	3,487,022	3,029,299
Employee stock purchase program
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	51,491	43,617
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