Basic and Diluted Net Loss per Common Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded because such instruments were anti-dilutive (in shares)	6,114	18,659
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded because such instruments were anti-dilutive (in shares)	2,066	1,595
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded because such instruments were anti-dilutive (in shares)	610	930
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded because such instruments were anti-dilutive (in shares)	1,819	14,515
Convertible notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded because such instruments were anti-dilutive (in shares)	1,619	1,619