Condensed Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		24 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Operating expenses:
Research and development	$ 2,680	$ 946	$ 10,173
General and administrative	2,495	2,020	11,155
Total operating expenses	5,175	2,966	21,328
Loss from operations	(5,175)	(2,966)	(21,328)
Interest income	18		37
Net loss	(5,157)	(2,966)	(21,291)
Accretion of convertible preferred stock to redemption value			(101)
Net loss applicable to common stockholders	(5,157)	(2,966)	(21,392)
Net loss per share applicable to common stockholders-basic and diluted (in dollars per share)	$ (0.39)	$ (2.14)	$ (4.33)
Weighted average number of common shares used in net loss per share applicable to common stockholders-basic and diluted (in shares)	13,345	1,383	4,943
Net loss	(5,157)	(2,966)	(21,291)
Other comprehensive income:
Unrealized gains on available-for-sale securities	7		1
Comprehensive loss	(5,150)	(2,966)	(21,290)
Non-cash stock-based compensation expenses included in operating expenses are as follows:
Stock-based compensation expense	837	259	2,565
Research and development
Non-cash stock-based compensation expenses included in operating expenses are as follows:
Stock-based compensation expense	426	236	1,838
General and administrative
Non-cash stock-based compensation expenses included in operating expenses are as follows:
Stock-based compensation expense	$ 411	$ 23	$ 727