Statement of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended			84 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Costs and expenses:
Research and development	$ 33,215	$ 6,792	$ 13,896	$ 108,107
General and administrative	14,210	6,889	5,738	41,559
Total costs and expenses	47,425	13,681	19,634	149,666
Loss from operations	(47,425)	(13,681)	(19,634)	(149,666)
Interest (expense) income	(1,454)	(507)	2	(1,482)
Loss on extinguishment of debt	(1,091)			(1,091)
Other loss	(1,175)	(374)	(30)	(1,546)
Change in fair value related to investor rights liability				683
Net loss before income tax benefit	(51,145)	(14,562)	(19,662)	(153,102)
Income tax benefit			1,029	1,327
Net loss	(51,145)	(14,562)	(18,633)	(151,775)
Add: accretion of preferred stock dividends	(5,891)	(7,063)	(6,838)	(33,046)
Net loss attributable to common stockholders	$ (57,036)	$ (21,625)	$ (25,471)	$ (184,821)
Net loss attributable to common stockholders per share :
Basic and diluted (in dollars per share)	$ (6.34)	$ (14.89)	$ (18.27)
Weighted average common shares outstanding:
Basic and diluted (in shares)	9,003	1,452	1,394