Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenue:
Collaboration revenue	$ 6,250	$ 6,251	$ 18,750	$ 13,542
Research and license fees	115	134	285	304
Total revenue	6,365	6,385	19,035	13,846
Operating expenses:
Research and development	16,649	8,706	42,043	21,237
General and administrative	6,648	3,836	17,924	9,441
Change in fair value of contingent consideration	78		78
Total operating expenses	23,375	12,542	60,045	30,678
Loss from operations	(17,010)	(6,157)	(41,010)	(16,832)
Other income (expense), net	(20)	44	48	(408)
Loss before income taxes	(17,030)	(6,113)	(40,962)	(17,240)
Benefit from income taxes			11,797
Net loss	(17,030)	(6,113)	(29,165)	(17,240)
Other comprehensive loss:
Unrealized loss on available-for-sale securities, net of tax	(74)		(74)
Comprehensive loss	$ (17,104)	$ (6,113)	$ (29,239)	$ (17,240)
Net loss per share - basic and diluted:	$ (0.61)	$ (0.26)	$ (1.14)	$ (1.96)
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	28,115	23,623	25,593	8,786