Intangible Assets

12 Months Ended

Dec. 31, 2015

Intangible Assets

Intangible Assets

4. Intangible Assets

Intangible assets consist of the following (in thousands):

	As of		As of
	December 31, 2015		December 31, 2014
Patents issued	$	6,180	$	6,518
Patents pending		1,156		3,373
Trademarks		40		40
Total intangible assets		7,376		9,931
Less patent amortization		(1,407)		(1,990)
Intangible assets, net	$	5,969	$	7,941

Amortization commences upon patent issuance. The useful life of the patents, once issued, will not exceed 20 years, and will depend on the nature of the patent. The average estimated amortization period of the Company's current portfolio is approximately 17 years from the date of patent issuance. The average estimated remaining amortization period of patents acquired from Symyx is approximately 3 years.

The following table presents patent amortization expense included in the Consolidated Statement of Operations (in thousands):

	Years Ended December 31,
	2015		2014		2013
Amortization expense	$	995	$	688	$	615

Estimated future aggregate annual amortization expense for both issued and pending intangible assets is as follows (in thousands):

As of December 31:
2016	$	580
2017		490
2018		430
2019		397
2020		379
Thereafter		3,653
Total	$	5,929