Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Collaboration revenue	$ 25,548	$ 25,072	$ 21,803
Grant revenue		34	34
Total revenue	25,548	25,106	21,837
Operating expenses:
Research and development	54,502	41,037	31,253
General and administrative	9,929	7,064	7,215
Total operating expenses	64,431	48,101	38,468
Loss from operations	(38,883)	(22,995)	(16,631)
Interest income	55	69	132
Loss before provision (benefit) for income taxes	(38,828)	(22,926)	(16,499)
Provision (benefit) for income taxes	579	(2,824)	7,207
Net loss	(39,407)	(20,102)	(23,706)
Cumulative preferred stock dividends	(4,162)	(7,190)	(3,100)
Net loss applicable to common stockholders	$ (43,569)	$ (27,292)	$ (26,806)
Net loss per share applicable to common stockholders - basic and diluted	$ (2.83)	$ (8.02)	$ (8.90)
Weighted-average number of common shares used in net loss per share applicable to common stockholders - basic and diluted	15,415,373	3,401,719	3,013,366