STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue:
Research and development revenue	$ 36,414	$ 47,310	$ 29,221
Costs and expenses:
Research and development	33,966	45,011	47,034
General and administrative	13,852	13,373	13,477
Total costs and expenses	47,818	58,384	60,511
Loss from operations	(11,404)	(11,074)	(31,290)
Interest income	445	317	619
Interest expense	(26)	(25)	(274)
Other income	113	20	266
Loss before income taxes	(10,872)	(10,762)	(30,679)
Benefit from income taxes			550
Net loss	(10,872)	(10,762)	(30,129)
Unrealized gain (loss) on marketable securities	108	1	(62)
Comprehensive loss	$ (10,764)	$ (10,761)	$ (30,191)
Basic and diluted net loss per share:
Net loss per share (in dollars per share)	$ (0.18)	$ (0.20)	$ (0.68)
Weighted average basic and diluted common shares outstanding (in shares)	59,821	52,778	44,529