COMPONENTS OF THE COMPANY'S CONDENSED CONSOLIDATED BALANCE SHEETS Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (2,163)	$ (3,130)
Other comprehensive income (loss) before reclassifications	(598)	(1,235)
Amounts reclassified from accumulated other comprehensive loss	(75)	51
Net-current period other comprehensive income (loss)	(673)	(1,184)
Ending balance	(2,836)	(4,314)
Unrealized Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	890	583
Other comprehensive income (loss) before reclassifications	(580)	(952)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net-current period other comprehensive income (loss)	(580)	(952)
Ending balance	310	(369)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,641)	(2,484)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	(75)	51
Net-current period other comprehensive income (loss)	(75)	51
Ending balance	(1,716)	(2,433)
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,412)	(1,229)
Other comprehensive income (loss) before reclassifications	(18)	(283)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net-current period other comprehensive income (loss)	(18)	(283)
Ending balance	$ (1,430)	$ (1,512)