G. INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible assets

Intangible assets consisted of the following for the periods indicated (in thousands):

	2017
	Gross		Accumulated		Intangible
	Amount		amortization		assets, net
Patents	$	6,524	$	(2,519)	$	4,005
Trademarks		14		(12)		2
Total intangible assets	$	6,538	$	(2,531)	$	4,007

	2016
	Gross		Accumulated		Intangible
	Amount		amortization		assets, net
Patents	$	5,987	$	(1,997)	$	3,990
Trademarks		14		(11)		3
Total intangible assets	$	6,001	$	(2,008)	$	3,993

Approximate amortization expense for intangible assets

At December 31, 2017, future amortization expense for intangible assets is estimated to be (in thousands):

2018	$	485
2019		485
2020		485
2021		486
2022		486
thereafter		1,580
	$	4,007