INCOME TAXES - Deferred Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Net operating loss carryforwards	$ 257,000	$ 417,000
Deferred revenues	0	1,000
Research and development tax credit carryforwards	57,000	53,000
Other	3,000	13,000
Total deferred tax assets before valuation allowance	317,000	484,000
Valuation allowance	(303,000)	(484,000)
Total deferred tax assets	14,000	0
Deferred tax liabilities
Debt issuance discount and other	(14,000)	0
Net deferred tax assets	0	0
Changes in valuation allowance
Increase (decrease) in valuation allowance	$ (181,200)	20,600	$ 4,700
Early adoption | ASU 2016-09
Changes in valuation allowance
Excess stock option tax benefits		$ 46,900