STOCKHOLDERS' EQUITY - Summary of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Foreign currency translation	$ (51,189)	$ (55,016)
Accumulated unrealized gain on marketable debt securities	25,037	15,746
Derivative instruments	14,087	19,688
Total accumulated other comprehensive loss	$ (12,065)	$ (19,582)

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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