Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Revenue:
Collaboration revenue	$ 6,344us-gaap_ContractsRevenue	$ 6,250us-gaap_ContractsRevenue
Research and license fees		85us-gaap_LicenseAndServicesRevenue
Total revenue	6,344us-gaap_Revenues	6,335us-gaap_Revenues
Operating expenses:
Research and development	23,719us-gaap_ResearchAndDevelopmentExpense	11,463us-gaap_ResearchAndDevelopmentExpense
General and administrative	7,336us-gaap_GeneralAndAdministrativeExpense	5,540us-gaap_GeneralAndAdministrativeExpense
Change in fair value of contingent consideration	215
Total operating expenses	31,270us-gaap_CostsAndExpenses	17,003us-gaap_CostsAndExpenses
Loss from operations	(24,926)us-gaap_OperatingIncomeLoss	(10,668)us-gaap_OperatingIncomeLoss
Other income, net	139us-gaap_NonoperatingIncomeExpense	59us-gaap_NonoperatingIncomeExpense
Net loss	(24,787)us-gaap_NetIncomeLoss	(10,609)us-gaap_NetIncomeLoss
Other comprehensive loss:
Unrealized loss on available-for-sale securities, net of tax	(52)
Comprehensive loss	$ (24,839)us-gaap_ComprehensiveIncomeNetOfTax	$ (10,609)us-gaap_ComprehensiveIncomeNetOfTax
Net loss per share - basic and diluted:	$ (0.76)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.44)us-gaap_EarningsPerShareBasicAndDiluted
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	32,558	24,148

Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

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