Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions
Revenue, Net	$ 33,047	$ 26,942	$ 12,053	$ 18,293	$ 23,037	$ 27,717	$ 20,089	$ 12,494
Income (Loss) From Operations	(30,785)	(29,518)	(33,893)	(42,485)	(31,330)	(34,933)	(37,021)	(33,871)	$ (136,681)	$ (137,155)	$ 1,468
Net Income (Loss) Attributable to Parent	$ (28,378)	$ (30,722)	$ (35,059)	$ (34,891)	$ (32,419)	$ (36,015)	$ (38,112)	$ (34,883)	$ (129,050)	$ (141,429)	$ (4,682)
Earnings Per Share, Basic and Diluted	$ (0.27)	$ (0.29)	$ (0.33)	$ (0.33)	$ (0.31)	$ (0.35)	$ (0.37)	$ (0.34)	$ (1.23)	$ (1.36)	$ (0.05)
Weighted Average Number of Shares Outstanding, Basic and Diluted	105,588	105,582	105,300	104,461	104,052	103,885	103,830	103,682	105,237	103,863	103,591