STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues:
Collaboration revenue								$ 8,066		$ 8,066	$ 56,786
Expenses:
Research and development expenses	10,051	9,764	9,237	9,835	8,863	8,181	7,591	7,303	38,887	31,938	28,495
General and administrative expenses	2,858	2,999	2,400	2,588	3,141	2,708	2,977	3,201	10,845	12,027	13,194
Total expenses	12,909	12,763	11,637	12,423	12,004	10,889	10,568	10,504	49,732	43,965	41,689
(Loss) income from operations	(12,909)	(12,763)	(11,637)	(12,423)	(12,004)	(10,889)	(10,568)	(2,438)	(49,732)	(35,899)	15,097
Other (expense) income, net	(33)	(47)	53	8	66	23	7	302	(19)	398	1,363
(Loss) income from operations before income taxes	(12,942)	(12,810)	(11,584)	(12,415)	(11,938)	(10,866)	(10,561)	(2,136)	(49,751)	(35,501)	16,460
Income tax benefit	2,273	5,812	355	381	298	271	264	53	8,821	886
Net (loss) income from continuing operations	(10,669)	(6,998)	(11,229)	(12,034)	(11,640)	(10,595)	(10,297)	(2,083)	(40,930)	(34,615)	16,460
Income (loss) from discontinued operations before income taxes	(76)	20,214	1,203	1,335	1,256	1,522	(112)	(459)	22,676	2,207	(1,166)
Income tax expense	30	(8,115)	(355)	(381)	(298)	(271)	(264)	(53)	(8,821)	(886)
Net income (loss) from discontinued operations	(46)	12,099	848	954	958	1,251	(376)	(512)	13,855	1,321	(1,166)
Net (loss) income	$ (10,715)	$ 5,101	$ (10,381)	$ (11,080)	$ (10,682)	$ (9,344)	$ (10,673)	$ (2,595)	$ (27,075)	$ (33,294)	$ 15,294
Net (loss) income per share - basic and diluted:
Net (loss) income from continuing operations (in dollars per share)	$ (0.17)	$ (0.11)	$ (0.18)	$ (0.19)	$ (0.19)	$ (0.17)	$ (0.20)	$ (0.04)	$ (0.65)	$ (0.60)	$ 0.42
Net income (loss) from discontinued operations (in dollars per share)		$ 0.19	$ 0.01	$ 0.01	$ 0.02	$ 0.02	$ (0.01)	$ (0.01)	$ 0.22	$ 0.02	$ (0.03)
Net (loss) income per share (in dollars per share)	$ (0.17)	$ 0.08	$ (0.17)	$ (0.18)	$ (0.17)	$ (0.15)	$ (0.21)	$ (0.05)	$ (0.43)	$ (0.58)	$ 0.39
Weighted average shares outstanding:
Basic and diluted (in shares)	62,817,495	62,815,549	62,805,662	62,798,008	62,790,223	62,778,575	51,968,667	51,719,187	62,809,219	57,359,466	38,874,721