Fair Value Measurements (Details) (Recurring [Member], USD $)	9 Months Ended
	Sep. 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	$ 5,144,000	$ 13,188,000
Short-term investments	17,000,000	24,000,000
Warrant liabilities	7,145,000	3,972,000
Level I [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	5,144,000	13,188,000
Short-term investments	17,000,000	24,000,000
Warrant liabilities	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 liabilities	0	0
Unrealized loss recognized	3,200,000
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 liabilities	$ 7,145,000	$ 3,972,000