ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications from Accumulated Other Comprehensive Income Included in Earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 427,569	$ 434,004	$ 511,545
Total reclassified and recognized in net loss, net of tax	(6,356)	(173)	(120)
Total other comprehensive income (loss), net of tax	(6,117)	1,700	244
Ending balance	207,163	427,569	434,004
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	6,661	4,961	4,717
Ending balance	544	6,661	4,961
Unrealized gain on marketable securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Total reclassified and recognized in net loss, net of tax	(6,358)	(193)	(481)
Unrealized gain reclassified and recognized in net loss, net of tax	164	1,864	773
Foreign currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Total reclassified and recognized in net loss, net of tax	2	20	361
Unrealized gain reclassified and recognized in net loss, net of tax	$ 75	$ 9	$ (409)