REVENUES - Schedule of Current Impact from Adoption on Consolidated Balance Sheet (Details) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
ASSETS
Contract assets	$ 8,474		$ 0
Non-current contract assets	12,760		0
LIABILITIES AND STOCKHOLDERS’ DEFICIT
Deferred revenues	5,837	$ 4,112	4,861
Other long-term liabilities	4,142	3,128	7,744
Accumulated deficit	(1,328,502)	(1,300,519)	(1,323,723)
Balances without Adoption of ASC 606
ASSETS
Contract assets	7,490
Non-current contract assets	12,153
LIABILITIES AND STOCKHOLDERS’ DEFICIT
Deferred revenues	5,271		4,861
Other long-term liabilities	3,341		7,744
Accumulated deficit	(1,328,726)		$ (1,323,723)
Effect of Change Higher/ (Lower) | Accounting Standards Update 2014-09
ASSETS
Contract assets	984
Non-current contract assets	607
LIABILITIES AND STOCKHOLDERS’ DEFICIT
Deferred revenues	566	(749)
Other long-term liabilities	801	(4,616)
Accumulated deficit	$ 224	$ 23,204