Intangible assets at December 31 were as follows:


December 31, 2023
Intangible Assets	Useful life	Gross Carrying Amount		Accumulated Amortization			Currency Exchange			Net
Amortized intangible assets
Patents	5-15 years	$	16,040	$	(15,699	)	$	(245	)	$	96
Developed product technology	2-10 years		169,499		(122,788	)		(6,192	)		40,519
Customer relationships	7-12 years		62,465		(46,656	)		(1,671	)		14,138
Software license and other	3-4 years		2,743		(2,677	)		(62	)		4
Total amortized intangible assets			250,747		(187,820	)		(8,170	)		54,757
Intangible assets with indefinite lives
In process research and development	Indefinite		-		-			-			-
Trademarks and trade names	Indefinite		10,303		-			(1,123	)		9,180
Total Intangible assets with indefinite lives			10,303		-			(1,123	)		9,180
Total intangible assets		$	261,050	$	(187,820	)	$	(9,293	)	$	63,937


December 31, 2022
Intangible Assets	Useful life	Gross Carrying Amount		Accumulated Amortization			Currency Exchange			Net
Amortized intangible assets
Patents	5-15 years	$	16,040	$	(15,437	)	$	(234	)	$	369
Developed product technology	2-10 years		169,499		(111,639	)		(6,176	)		51,684
Customer relationships	7-12 years		62,465		(42,784	)		(1,672	)		18,009
Software license and other	3-4 years		2,743		(2,677	)		(59	)		7
Total amortized intangible assets			250,747		(172,537	)		(8,141	)		70,069
Intangible assets with indefinite lives
In process research and development	Indefinite		-		-			-			-
Trademarks and trade names	Indefinite		10,303		-			(1,235	)		9,068
Total Intangible assets with indefinite lives			10,303		-			(1,235	)		9,068
Total intangible assets		$	261,050	$	(172,537	)	$	(9,376	)	$	79,137

Amortization expense related to intangible assets subject to amortization was $15.3 million, $15.6 million and $16.2 million for the twelve months ended December 31, 2023, 2022 and 2021, respectively. In process research and development is transferred to amortized intangible assets at the time the product becomes viable.

The weighted amortization period for intangible assets subject to amortization is 9.9 years. The schedule below sets future amortization expense of our currently owned intangible assets: