Fair Value Measurements (Details 3) (USD $)	0 Months Ended	12 Months Ended			84 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 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
Charge related to change in fair value of warrant liability		1,181,000	366,000	7,000	1,563,000
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	193,000
Change in fair value of warrant liability		379,000	330,000
Conversion of warrant liability to equity		(902,000)
Balance at the end of the period			523,000
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	407,000
Change in fair value of warrant liability		802,000	36,000
Conversion of warrant liability to equity		(1,277,000)
Balance at the end of the period			$ 443,000