Condensed Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Collaboration and license revenue	$ 2,427	$ 2,766	$ 7,213	$ 8,474
Operating expenses:
Research and development	31,780	18,088	88,918	56,642
General and administrative	6,424	3,907	16,601	10,654
Total operating expenses	38,204	21,995	105,519	67,296
Loss from operations	(35,777)	(19,229)	(98,306)	(58,822)
Interest and other (expense) income, net	(16)	679	437	532
Net loss	$ (35,793)	$ (18,550)	$ (97,869)	$ (58,290)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.86)	$ (0.53)	$ (2.37)	$ (3.39)
Shares used to compute net loss per share attributable to common stockholders:
Basic and diluted	41,402,037	35,200,761	41,233,206	17,218,475

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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Revenue from multiple-deliverable arrangements that include licensing fees and services revenue. Licensing revenue is consideration received from another party for the right to use, but not own, certain of the entity's intangible assets. Licensing arrangements include, but are not limited to, rights to use a patent, copyright, technology, manufacturing process, software or trademark. Licensing fees are generally, but not always, fixed as to amount and not dependent upon the revenue generated by the licensing party. An entity may receive licensing fees for licenses that also generate royalty payments to the entity. Services revenue may be derived by providing other, nonspecified, services during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

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Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

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The net result for the period of deducting operating expenses from operating revenues.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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