COMPONENTS OF THE COMPANY'S CONDENSED CONSOLIDATED BALANCE SHEETS Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (4,314)	$ (1,361)	$ (3,130)	$ (1,689)
Other comprehensive income (loss) before reclassifications	2,536	7	1,301	319
Amounts reclassified from accumulated other comprehensive loss	58	18	109	34
Net-current period other comprehensive income (loss)	2,594	25	1,410	353
Ending balance	(1,720)	(1,336)	(1,720)	(1,336)
Unrealized Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(369)	68	583	(266)
Other comprehensive income (loss) before reclassifications	2,566	257	1,614	591
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net-current period other comprehensive income (loss)	2,566	257	1,614	591
Ending balance	2,197	325	2,197	325
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(2,433)	(696)	(2,484)	(712)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive loss	58	18	109	34
Net-current period other comprehensive income (loss)	58	18	109	34
Ending balance	(2,375)	(678)	(2,375)	(678)
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,512)	(733)	(1,229)	(711)
Other comprehensive income (loss) before reclassifications	(30)	(250)	(313)	(272)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net-current period other comprehensive income (loss)	(30)	(250)	(313)	(272)
Ending balance	$ (1,542)	$ (983)	$ (1,542)	$ (983)