Condensed Consolidated Statements of Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Consolidated Statements of Comprehensive Loss
Contract revenue		$ 16
Operating expenses:
Research and development	7,690	6,320
General and administrative	2,470	2,019
Total operating expenses	10,160	8,339
Loss from operations	(10,160)	(8,323)
Other income (expense):
Interest expense	(260)	(263)
Interest and other income, net	12	12
Net loss	(10,408)	(8,574)
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities	(4)
Comprehensive loss	$ (10,412)	$ (8,574)
Basic and diluted net loss per common share (in dollars per share)	$ (0.32)	$ (0.55)
Weighted average common shares outstanding used to calculate basic and diluted net loss per common share (in shares)	32,966,471	15,607,379