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, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (2,382)		$ (2,514)		$ (2,139)		$ (2,710)
Other comprehensive income before reclassifications	263		46		(12)		193
Amounts reclassified from accumulated other comprehensive loss	31		49		63		98
Net-current period other comprehensive income	294		95		51		291
Ending balance	(2,088)		(2,419)		(2,088)		(2,419)
Unrealized Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(665)		(137)		(427)		(220)
Other comprehensive income before reclassifications	226		15		(12)		98
Amounts reclassified from accumulated other comprehensive loss	0		0		0		0
Net-current period other comprehensive income	226		15		(12)		98
Ending balance	(439)		(122)		(439)		(122)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,205)		(1,887)		(1,237)		(1,936)
Other comprehensive income before reclassifications	0		0		0		0
Amounts reclassified from accumulated other comprehensive loss	31	[1]	49	[1]	63	[2]	98	[2]
Net-current period other comprehensive income	31		49		63		98
Ending balance	(1,174)		(1,838)		(1,174)		(1,838)
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(512)		(490)		(475)		(554)
Other comprehensive income before reclassifications	37		31		0		95
Amounts reclassified from accumulated other comprehensive loss	0		0		0		0
Net-current period other comprehensive income	37		31		0		95
Ending balance	$ (475)		$ (459)		$ (475)		$ (459)

[1] This component of accumulated other comprehensive income (loss) is included in the computation of net periodic pension cost for the three months ended June 30, 2018 and 2017.

[2] This component of accumulated other comprehensive income (loss) is included in the computation of net periodic pension cost for the six months ended June 30, 2018 and 2017.