Summary of Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of Quarterly Financial Data (unaudited)
Total revenues	$ 890	$ 855	$ 1,706	$ 1,943	$ 1,397	$ 674	$ 923	$ 39,322	$ 5,394	$ 42,316	$ 1,425
Income (loss) from operations	(8,618)	(7,242)	(7,857)	(6,785)	(9,520)	(7,743)	(7,957)	28,823	(30,502)	3,603	(38,861)
Net income (loss)	(8,626)	(7,251)	(7,866)	(6,763)	(9,517)	(7,745)	(7,948)	28,840	(30,506)	3,630	(38,785)
Basic net income (loss) per share (in dollars per share)	$ (0.24)	$ (0.21)	$ (0.23)	$ (0.20)	$ (0.28)	$ (0.23)	$ (0.23)	$ 0.84	$ (0.88)	$ 0.11	$ (1.24)
Diluted net income (loss) per share (in dollars per share)	$ (0.24)	$ (0.21)	$ (0.23)	$ (0.20)	$ (0.28)	$ (0.23)	$ (0.23)	$ 0.84	$ (0.88)	$ 0.11	$ (1.24)
Summary of quarterly financial data
Deferred revenue recognized associated with termination of agreement										38,885
Commercial Alliance Agreement | Archer Daniels Midland
Summary of quarterly financial data
Deferred revenue recognized associated with termination of agreement								$ 38,885