ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Description of Business
Number of operating segments | segment			2
Effect of Adoption of ASC Topic 606
General and administrative expenses	$ 26,523	$ 25,227	$ 52,159	$ 50,613
Non-service defined benefit plan expense	176	184	352	368
Deferred tax assets	74,897		74,897			$ 68,394	$ 68,126
Accrued expenses and other current liabilities	54,258		54,258			67,335	66,308
Accumulated deficit	(370,221)		(370,221)			(360,531)	(359,772)
ASU 2017-07
Effect of Adoption of ASC Topic 606
General and administrative expenses	(200)	(200)	(400)	(400)
Non-service defined benefit plan expense	200	$ 200	400	$ 400
Before adoption of ASC 606 | ASU 2014-09
Effect of Adoption of ASC Topic 606
Deferred tax assets					$ 74,900		74,624
Accrued expenses and other current liabilities					54,267		53,210
Accumulated deficit					(370,227)		(369,446)
Adjustments | ASU 2014-09
Effect of Adoption of ASC Topic 606
Contract liability	$ 1,000		$ 1,000
Deferred tax assets					3	268	(273)
Accrued expenses and other current liabilities					9	1,027	(1,048)
Accumulated deficit					$ (6)	$ (759)	$ 775