INCOME TAXES - SUMMARY (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income tax benefit (provision):
Federal									$ 45,518	$ 46,598	$ 43,536
State									7,268	10,642	7,328
Foreign									1,124
Expiration of Net Operating Losses and Research & Development Tax Credits										(155)	(2,302)
Income tax benefit (provision) before valuation allowance									53,910	57,085	48,562
Deferred tax valuation allowance									$ (53,910)	(57,085)	(48,562)
Reconciliation between the amount of reported income tax and the amount computed using U.S. Statutory rate
U.S. Statutory rate (as a percent)									34.00%
Pre-tax loss	$ (32,307)	$ (29,598)	$ (31,952)	$ (34,673)	$ (32,684)	$ (31,980)	$ (32,359)	$ (30,174)	$ (128,530)	(127,197)	(118,080)
Loss at Statutory Rates									(43,700)	(43,247)	(40,147)
Difference in Foreign Tax Rates									150
Research and Development Credits									(5,203)	(4,935)	(4,126)
State Taxes									(7,268)	(10,642)	(7,328)
Other									2,111	1,584	737
Expiration of Net Operating Losses and Research & Development Tax Credits										155	2,302
Change in Valuation Allowance									53,910	57,085	$ 48,562
Foreign pre-tax loss									3,700
Gross Deferred Tax Assets
Net Operating Loss Carryforwards	174,555				180,777				174,555	180,777
Foreign Net Operating Loss Carryforwards	1,124								1,124
Tax Credit Carryforwards	32,306				35,895				32,306	35,895
Deferred Research and Development Expenses	109,520				48,608				109,520	48,608
Stock-based Compensation	12,362				8,393				12,362	8,393
Fixed Assets	1,526				2,017				1,526	2,017
Deferred Revenue	1,418				1,703				1,418	1,703
Accrued Expenses and Other	894				219				894	219
Gross Deferred Tax Assets	333,705				277,612				333,705	277,612
Gross Deferred Tax Liabilities
Other Acquired Intangibles	(2,868)				(3,382)				(2,868)	(3,382)
IPR&D Intangibles	(28,054)				(4,661)				(28,054)	(4,661)
Gross Deferred Tax Liabilities	(30,922)				(8,043)				(30,922)	(8,043)
Total Deferred Tax Assets and Liabilities	302,783				269,569				302,783	269,569
Deferred Tax Assets Valuation Allowance	(330,837)				(274,230)				(330,837)	(274,230)
Net Deferred Tax Asset (Liability)	$ (28,054)				$ (4,661)				$ (28,054)	$ (4,661)