CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 15,381	$ 13,902	$ 29,581	$ 28,001
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in each of the three and six months ended June 30, 2018 and 2017	37	31	0	95
Unrealized gain (loss) on marketable securities, net of $0 tax in each of the three and six months ended June 30, 2018 and 2017	226	15	(12)	98
Amortization of defined benefit pension items, net of tax of $9 and $18 in the three and six months ended June 30, 2018, respectively, and $14 and $27 in the three and six months ended June 30, 2017, respectively	31	49	63	98
Total other comprehensive income	294	95	51	291
TOTAL COMPREHENSIVE INCOME	$ 15,675	$ 13,997	$ 29,632	$ 28,292