GEOGRAPHIC AND SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($) ReportableSegments	Dec. 31, 2017 USD ($)
Number of reportable operating segment	3	3
Long-term assets	$ 24,848	$ 25,778	$ 42,400
United States
Long-term assets	$ 24,400	$ 25,800	$ 24,400
Percentage of assets (as a percent)	100.00%	100.00%	58.00%

Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer.

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+ Details