Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 82	$ 79	$ 137	$ 194	$ 56	$ 20	$ 58	$ 46	$ 270	$ 170	$ 200
Total cost of revenue	209	204	162	147	460	512	547	793	426	2,312	7,501
Gross loss	(127)	(125)	(25)	47	(404)	(492)	(489)	(747)	(230)	(2,132)	(7,301)
Operating expenses	16,234	6,698	7,334	6,911	5,763	5,699	6,107	10,253
Other income (expense)	(1,290)	5,302	603	(1,661)	2,795	179	4,339	(3,009)
Net loss	$ (17,651)	$ (1,521)	$ (6,756)	$ (8,525)	$ (3,372)	$ (6,012)	$ (2,257)	$ (14,009)	$ (34,453)	$ (25,650)	$ (31,554)
Basic net loss per share (in dollars per share)	$ (0.40)	$ (0.04)	$ (0.17)	$ (0.21)	$ (0.08)	$ (0.15)	$ (0.06)	$ (0.35)	$ (0.82)	$ (0.63)	$ (1.06)
Diluted net loss per share (in dollars per share)	$ (0.40)	$ (0.07)	$ (0.17)	$ (0.21)	$ (0.09)	$ (0.17)	$ (0.09)	$ (0.35)	$ (0.85)	$ (0.70)	$ (1.12)