Fair Value Measurements (Details) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	$ 10,384	$ 13,188
Short-term investments	17,000	24,000
Warrant liability	3,134	3,972
Level I [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	10,384	13,188
Short-term investments	17,000	24,000
Warrant liability	0	0
Level II [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	0	0
Short-term investments	0	0
Warrant liability	0	0
Level III [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	0	0
Short-term investments	0	0
Warrant liability	$ 3,134	$ 3,972