COMPONENTS OF THE COMPANY'S CONDENSED CONSOLIDATED BALANCE SHEETS Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (2,139)	$ (2,710)
Other comprehensive income (loss) before reclassifications	(275)	147
Amounts reclassified from accumulated other comprehensive loss	32	49
Net-current period other comprehensive income (loss)	(243)	196
Ending balance	(2,382)	(2,514)
Unrealized Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(427)	(220)
Other comprehensive income (loss) before reclassifications	(238)	83
Amounts reclassified from accumulated other comprehensive loss	0	0
Net-current period other comprehensive income (loss)	(238)	83
Ending balance	(665)	(137)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,237)	(1,936)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	32	49
Net-current period other comprehensive income (loss)	32	49
Ending balance	(1,205)	(1,887)
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(475)	(554)
Other comprehensive income (loss) before reclassifications	(37)	64
Amounts reclassified from accumulated other comprehensive loss	0	0
Net-current period other comprehensive income (loss)	(37)	64
Ending balance	$ (512)	$ (490)