Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions
Revenues	$ 21,482	$ 419	$ 676	$ 277	$ 1,410	$ 238	$ 214	$ 360	$ 22,854	$ 2,222	$ 1,089
Loss From Operations	(3,447)	(40,336)	(26,111)	(30,472)	(16,976)	(31,216)	(28,624)	(25,555)	(100,366)	(102,371)	(108,415)
Consolidated Net Loss	$ (2,933)	$ (40,498)	$ (26,028)	$ (30,835)	$ (17,414)	$ (31,658)	$ (29,080)	$ (25,974)	$ (100,294)	$ (104,126)	$ (110,211)
Consolidated Net Loss Per Common Share, Basic and Diluted	$ 0.00	$ (0.08)	$ (0.05)	$ (0.06)	$ (0.03)	$ (0.06)	$ (0.06)	$ (0.05)	$ (0.19)	$ (0.20)	$ (0.23)
Shares Used In Computing Consolidated Net Loss Per Common Share Basic And Diluted	593,694	514,796	514,623	513,955	513,523	513,419	513,083	512,428	534,432	513,117	489,707