Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions
Revenues	$ 1,410	$ 238	$ 214	$ 360	$ 218	$ 372	$ 199	$ 300	$ 2,222	$ 1,089	$ 1,849
Loss From Operations	(16,976)	(31,216)	(28,624)	(25,555)	(24,492)	(29,060)	(25,480)	(29,383)	(102,371)	(108,415)	(114,095)
Consolidated Net Loss	$ (17,414)	$ (31,658)	$ (29,080)	$ (25,974)	$ (24,873)	$ (29,539)	$ (25,931)	$ (29,868)	$ (104,126)	$ (110,211)	$ (116,215)
Consolidated Net Loss Per Common Share, Basic and Diluted	$ (0.03)	$ (0.06)	$ (0.06)	$ (0.05)	$ (0.05)	$ (0.06)	$ (0.05)	$ (0.06)	$ (0.20)	$ (0.23)	$ (0.34)
Shares Used In Computing Consolidated Net Loss Per Common Share Basic And Diluted	513,523	513,419	513,083	512,428	507,619	490,049	480,634	480,324	513,117	489,707	340,761