ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications from Accumulated Other Comprehensive Income Included in Earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 207,163	$ 427,569
Total reclassified and recognized in net loss, net of tax	(544)	(6,356)
Total other comprehensive loss, net of tax	(544)	(6,117)
Ending balance	176,624	207,163
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	544	6,661
Ending balance	0	544
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	(544)	(6,358)
Unrealized gain reclassified and recognized in net loss, net of tax	0	164
Foreign currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Total reclassified and recognized in net loss, net of tax	0	2
Unrealized gain reclassified and recognized in net loss, net of tax	$ 0	$ 75