CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Revenue:
Research and development revenue	$ 5,661	$ 8,498
Costs and expenses:
Research and development	8,181	9,303
General and administrative	3,400	3,599
Total costs and expenses	11,581	12,902
Loss from operations	(5,920)	(4,404)
Interest income	151	65
Interest expense	(4)	(6)
Other income (expense)	(2)	85
Net loss	(5,775)	(4,260)
Unrealized gain on marketable securities	9	19
Comprehensive loss	$ (5,766)	$ (4,241)
Basic and diluted net loss per share:
Net loss per share (in dollars per share)	$ (0.09)	$ (0.08)
Weighted average basic and diluted common shares outstanding (in shares)	62,384	53,810