Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement [Abstract]
Revenues-related party	$ 167	$ 735	$ 338	$ 1,139
Operating expenses:
Research and development	8,147	8,019	14,104	16,776
General and administrative	3,212	2,427	6,393	4,885
Total operating expenses	11,359	10,446	20,497	21,661
Loss from operations	(11,192)	(9,711)	(20,159)	(20,522)
Interest income, net	14		36
Loss before income taxes	(11,178)	(9,711)	(20,123)	(20,522)
Provision for income taxes	124		130
Net loss	$ (11,302)	$ (9,711)	$ (20,253)	$ (20,522)
Basic and diluted net loss per share	$ (0.64)	$ (0.67)	$ (1.15)	$ (1.42)
Shares used to compute basic and diluted net loss per share	17,679	14,497	17,679	14,497