Note 6 Intangible Assets

Intangible assets other than goodwill at December 31, 2015 and December 31, 2014 are as follows:



	2015						2014
(in thousands)	Gross		Accumulated Amortization		Net		Gross		Accumulated Amortization		Net		Useful Life (in years)	Weighted Average Useful Life Remaining (in years)
Intangible assets with finite lives:
Licenses	$	—	$	—	$	—	$	5,875	$	(5,875)	$	—	N/A	N/A
Patent costs		16,251		(4,895)		11,356		20,733		(7,369)		13,364	1-19	8
Acquired technology		52,809		(16,405)		36,404		57,383		(18,241)		39,142	2-15	4
Internally developed software		4,730		(2,919)		1,811		9,073		(5,517)		3,556	3	3
Customer relationships		101,933		(36,158)		65,775		157,139		(36,975)		120,164	2-15	7
Non-compete agreements		12,163		(8,558)		3,605		35,469		(11,784)		23,685	2-5	3
Trade names		28,108		(12,498)		15,610		21,800		(4,455)		17,345	1-9	6
Other		46,435		(23,530)		22,905		39,100		(6,905)		32,195	1-7	5
Intangible assets with indefinite lives:
Trademarks		—		—		—		2,110		—		2,110	N/A	N/A
Total intangible assets	$	262,429	$	(104,963)	$	157,466	$	348,682	$	(97,121)	$	251,561	1-19	5

Amortization expense related to costs incurred to internally develop and extend patents in the United States and various other countries was $303, $281 and $250 for the years ended December 31, 2015, 2014 and 2013, respectively.

Amortization expense related to all other intangible assets was $60,763, $39,203 and $20,447 for the years ended December 31, 2015, 2014 and 2013, respectively. Amortization of these intangible assets is calculated on a straight-line basis over periods ranging from one year to nineteen years.

Annual amortization expense for intangible assets is expected to be $35,113 in 2016, $32,087 in 2017, $26,920 in 2018, $21,606 in 2019 and $16,912 in 2020.

During the fourth quarter of 2015, the Company recorded impairment charges of $93,520, reflecting $92,248 of impairment charges related to the Company’s Americas reporting unit and $1,272 of impairment charges related to the Company’s EMEA reporting unit. Further, impairment charges reflected approximately $63,852 of charges to customer relationships, $19,164 of charges to acquired technology, $5,952 of charges to trade names, $3,416 of charges to non-compete agreements, $791 of charges to other intangibles and $345 of charges to internally developed software.

The impairment charges were measured as the difference between the carrying amount of the assets and their fair value. The fair value of the assets was determined under the income approach based on a discounted cash flow model using updated future revenue and operating income projections. In addition to impairment charges, gross intangible assets were negatively impacted by foreign currency translation. See Note 2 to the Consolidated Financial Statements.