STOCKHOLDERS' EQUITY - Summary of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Equity [Abstract]
Foreign currency translation	$ (53,641)	$ (45,580)
Accumulated unrealized gain on marketable debt securities	18,618	802
Other	27,076	9,658
Total accumulated other comprehensive loss	$ (7,947)	$ (35,120)

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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