Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues
Collaborative revenues	$ 1,145	$ 4,907	$ 2,067
Operating expenses
Research and development (includes stock-based compensation of $2,208, $680, and $512, respectively)	26,722	18,794	17,309
General and administrative (includes stock-based compensation of $3,503, $1,250, and $1,086, respectively)	12,720	6,999	7,610
Total operating expenses	39,442	25,793	24,919
Loss from operations	(38,297)	(20,886)	(22,852)
Interest income, net	349	37	87
Net loss	$ (37,948)	$ (20,849)	$ (22,765)
Net loss per common share, basic and diluted	$ (0.44)	$ (0.38)	$ (0.44)
Weighted average common shares outstanding, basic and diluted	85,715	55,116	52,183