3. Patents and Licenses

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Patents and Licenses

Purchased patents and licenses paid for the use of other entities’ patents are amortized over the useful life of the patent or license. The following tables provide information regarding patents and licenses (dollars in thousands):

December 31, 2017						December 31, 2016
Weighted Average Original Life (years)		Gross Carrying Amount		Accumulated Amortization		Weighted Average Original Life (years)		Gross Carrying Amount		Accumulated Amortization
	15.67	$	13,840	$	12,062		15.67	$	13,840	$	11,911

Aggregate amortization expense for patents and licenses was $151,000, $264,000 and $345,000 for 2017, 2016 and 2015, respectively. Estimated future amortization expense for each of the years set forth below ending December 31 is as follows (in thousands):

2018	$	119
2019	$	119
2020	$	119
2021	$	119
2022	$	117