ACCUMULATED OTHER COMPREHENSIVE LOSS, Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accumulated other comprehensive loss [Abstract]
Foreign currency translation adjustment, net of taxes of ($826) at March 31, 2018 and ($801) at December 31, 2017	$ (12,520)	$ (16,537)
Unrealized holding gains on available-for-sale securities, net of taxes of $65 at March 31, 2018 and $85 at December 31, 2017	114	145
Unfunded SERP liability, net of taxes of ($1,609) at March 31, 2018 and ($1,635) at December 31, 2017	(3,147)	(3,233)
Accumulated other comprehensive loss	(15,553)	(19,625)
Accumulated other comprehensive loss, tax [Abstract]
Foreign currency translation adjustment, tax	(826)	(801)
Unrealized holding gains on available-for-sale securities, tax	65	85
Change in unfunded SERP liability, tax	$ (1,609)	$ (1,635)