Selected Quarterly Financial Information (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended	84 Months Ended
Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 30, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Selected Quarterly Financial Information (unaudited)
Research and development	$ 15,379	$ 11,101	$ 4,345	$ 2,390	$ 1,998	$ 1,595	$ 1,578	$ 1,621	$ 33,215	$ 6,792	$ 13,896	$ 108,107
General and administrative	5,065	4,166	3,241	1,738	1,548	2,259	1,694	1,388	14,210	6,889	5,738	41,559
Loss from operations	(20,444)	(15,267)	(7,586)	(4,128)	(3,546)	(3,854)	(3,272)	(3,009)	(47,425)	(13,681)	(19,634)	(149,666)
Net loss attributable to common stockholders	$ (20,388)	$ (18,424)	$ (11,863)	$ (6,361)	$ (5,606)	$ (5,928)	$ (5,326)	$ (4,765)	$ (57,036)	$ (21,625)	$ (25,471)	$ (184,821)
Basic and diluted earnings per common share (in dollars per share)	$ (0.65)	$ (10.26)	$ (8.07)	$ (4.33)	$ (3.81)	$ (4.07)	$ (3.68)	$ (3.31)	$ (6.34)	$ (14.89)	$ (18.27)

- Definition

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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