Net Loss per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Components of basic and diluted net loss per share
Net loss	$ (7,102)	$ (3,895)
Weighted average common shares outstanding	21,824	21,544
Net loss per share:
Basic and diluted (in dollars per share)	$ (0.33)	$ (0.18)
Anti-dilutive securities excluded from the computation of diluted net loss per share
Anti-dilutive securities (in shares)	11,198	3,260
Stock options
Anti-dilutive securities excluded from the computation of diluted net loss per share
Anti-dilutive securities (in shares)	3,335	2,750
Shares of common stock issuable upon the vesting of restricted stock units
Anti-dilutive securities excluded from the computation of diluted net loss per share
Anti-dilutive securities (in shares)	481	510
Warrants
Anti-dilutive securities excluded from the computation of diluted net loss per share
Anti-dilutive securities (in shares)	7,382