Intangible assets subject to amortization at December 31 were as follows:


December 31, 2021
Intangible Assets	Useful life	Gross Carrying Amount		Accumulated Amortization			Currency Exchange			Net
Amortized intangible assets
Patents	5-15 years	$	16,040	$	(15,242	)	$	(97	)	$	701
Developed product technology	2-10 years		166,819		(100,248	)		(5,736	)		60,835
Customer relationships	7-12 years		62,093		(38,760	)		(1,688	)		21,645
Software license and other	3-4 years		2,743		(2,677	)		(61	)		5
Total amortized intangible assets			247,695		(156,927	)		(7,582	)		83,186
Intangible assets with indefinite lives
In process research and development	Indefinite		2,061		-			-			2,061
Trademarks and trade names	Indefinite		10,303		-			(1,000	)		9,303
Total Intangible assets with indefinite lives			12,364		-			(1,000	)		11,364
Total intangible assets		$	260,059	$	(156,927	)	$	(8,582	)	$	94,550


December 31, 2020
Intangible Assets	Useful life	Gross Carrying Amount		Accumulated Amortization			Currency Exchange			Net
Amortized intangible assets
Patents	5-15 years	$	13,040	$	(11,409	)	$	(139	)	$	1,492
Developed product technology	2-10 years		164,300		(89,027	)		(5,891	)		69,382
Customer relationships	7-12 years		62,093		(34,597	)		(1,688	)		25,808
Software license and other	3-4 years		5,743		(5,677	)		(63	)		3
Total amortized intangible assets			245,176		(140,710	)		(7,781	)		96,685
Intangible assets with indefinite lives
In process research and development	Indefinite		4,580		-			-			4,580
Trademarks and trade names	Indefinite		10,303		-			(977	)		9,326
Total Intangible assets with indefinite lives			14,883		-			(977	)		13,906
Total intangible assets		$	260,059	$	(140,710	)	$	(8,758	)	$	110,591

Amortization expense related to intangible assets subject to amortization was $16.2 million, $16.3 million and $18.0 million for the years ended December 31, 2021, 2020 and 2019, 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: