Basis of Presentation , Accounting Policies and Going Concern (Details) - USD ($) $ 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	Dec. 31, 2012
Changes in operating assets and liabilities:
Net Cash used in Operating Activities									$ (100,989)	$ (89,064)	$ (52,631)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract]
Net Cash provided by Financing Activities									16,422	217,122	89,230
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	$ 61,653				$ 146,470				61,653	146,470	18,130	$ 12,416
Available-for-sale securities	50,097				49,897				50,097	49,897
Net realized gains or losses									0	0
Working capital	95,500								95,500
Nonoperating Income (Expense) [Abstract]
Net loss	(30,446)	$ (25,997)	$ (33,668)	$ (27,389)	(30,555)	$ (23,008)	$ (25,920)	$ (16,225)	(117,500)	(95,708)	$ (62,124)
Research and Development
Prepaid research and development costs	$ 3,100				$ 3,700				$ 3,100	$ 3,700
Furniture and equipment | Minimum
Cash, Cash Equivalents and Marketable Securities
Estimated useful lives									2 years
Furniture and equipment | Maximum
Cash, Cash Equivalents and Marketable Securities
Estimated useful lives									5 years