Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per 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
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 218	$ 372	$ 199	$ 300	$ 343	$ 355	$ 555	$ 596	$ 1,089	$ 1,849	$ 4,908
Loss From Operations	(24,492)	(29,060)	(25,480)	(29,383)	(33,342)	(25,691)	(25,926)	(29,136)	(108,415)	(114,095)	(95,718)
Consolidated Net Loss	$ (24,873)	$ (29,539)	$ (25,931)	$ (29,868)	$ (33,845)	$ (26,103)	$ (26,638)	$ (29,629)	$ (110,211)	$ (116,215)	$ (101,775)
Consolidated Net Loss Per Common Share, Basic and Diluted	$ (0.05)	$ (0.06)	$ (0.05)	$ (0.06)	$ (0.10)	$ (0.08)	$ (0.08)	$ (0.09)	$ (0.23)	$ (0.34)	$ (0.34)
Shares Used In Computing Consolidated Net Loss Per Common Share Basic And Diluted	507,619	490,049	480,634	480,324	350,069	337,678	337,668	337,527	489,707	340,761	302,844