ACCUMULATED OTHER COMPREHENSIVE LOSS, Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated other comprehensive loss [Abstract]
Foreign currency translation adjustment	$ (16,537)	$ (28,976)	$ (19,305)
Unrealized holding gain on available-for-sale securities, net of taxes of $85, $263 and $265 as of December 31, 2017, 2016 and 2015	145	424	434
Unfunded SERP liability, net of taxes of ($1,635), ($1,398) and ($1,327) as of December 31, 2017, 2016 and 2015	(3,233)	(2,745)	(3,005)
Accumulated other comprehensive loss	(19,625)	(31,297)	(21,876)
Accumulated other comprehensive loss, tax [Abstract]
Unrealized holding gains on available-for-sale securities, tax	85	263	265
Change in unfunded SERP liability, tax	$ (1,635)	$ (1,398)	$ (1,327)