REVENUES - Schedule of Current Impact from Adoption on Consolidated Balance Sheet (Details) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
ASSETS
Contract assets	$ 8,026		$ 0
Non-current contract assets	12,756		0
LIABILITIES AND STOCKHOLDERS’ DEFICIT
Deferred revenues	4,696	$ 4,112	4,861
Other long-term liabilities	4,060	3,128	7,744
Accumulated deficit	(1,343,609)	(1,300,519)	(1,323,723)
Balances without Adoption of ASC 606
ASSETS
Contract assets	8,022
Non-current contract assets	12,756
LIABILITIES AND STOCKHOLDERS’ DEFICIT
Deferred revenues	4,771		4,861
Other long-term liabilities	4,060		7,744
Accumulated deficit	(1,343,534)		$ (1,323,723)
Effect of Change Higher/ (Lower) | Accounting Standards Update 2014-09
ASSETS
Contract assets	4
Non-current contract assets	0
LIABILITIES AND STOCKHOLDERS’ DEFICIT
Deferred revenues	(75)	(749)
Other long-term liabilities	0	(4,616)
Accumulated deficit	$ (75)	$ 23,204