Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenues	$ 9,666	$ 5,145	$ 11,686
Operating expenses:
Research and development	101,706	63,764	73,768
General and administrative	23,675	19,211	20,916
Total operating expenses	125,381	82,975	94,684
Loss from operations	(115,715)	(77,830)	(82,998)
Other income (expense):
Other income (expense)	963	350	(191)
Other income (expense), net	963	350	(191)
Net loss	$ (114,752)	$ (77,480)	$ (83,189)
Net loss per share-basic and diluted	$ (2.63)	$ (2.11)	$ (2.36)
Weighted-average number of common shares used in net loss per share-basic and diluted	43,582	36,704	35,261
Comprehensive loss	$ (114,752)	$ (77,480)	$ (83,189)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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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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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. Excludes 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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Amount of income (expense) related to nonoperating activities, classified as other.

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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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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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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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