Fair Value Measurements (Details 3) (USD $)	3 Months Ended		9 Months Ended		81 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Changes in fair value of the Company's Level 3 valuation for the Series A and Series B warrant liabilities
Public offering price (in dollars per share)			$ 22.00
Fair value of warrant liability reclassified to additional paid-in capital	$ 2,200,000		$ 2,200,000		$ 2,200,000
Charge related to the conversion of warrant liability to equity	970,000	69,000	1,231,000	340,000	1,602,000
Series A Warrant
Changes in fair value of the Company's Level 3 valuation for the Series A and Series B warrant liabilities
Balance at the beginning of the period			523,000
Change in fair value of warrant liability			379,000
Conversion of warrant liability to equity			(902,000)
Series B Warrant
Changes in fair value of the Company's Level 3 valuation for the Series A and Series B warrant liabilities
Balance at the beginning of the period			443,000
Warrants issued in connection with venture debt facility			32,000
Change in fair value of warrant liability			852,000
Conversion of warrant liability to equity			$ (1,327,000)