OTHER INCOME, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OTHER INCOME, NET
Interest and dividend income	$ 2,851	$ 2,130	$ 1,421
Gains on trading securities relating to deferred compensation plans	9,977	4,275	1,450
Interest expense	(144)	(105)	(76)
Foreign exchange gains (losses)	259	(955)	(1,427)
Capital gains (losses)	25	7	2
Miscellaneous, net	177	146	126
Total other income, net	$ 13,145	$ 5,498	$ 1,496