Intangible assets are recorded at cost, or when acquired as a part of a business combination, at estimated fair value, less accumulated amortization. These assets are amortized on a straight-line basis over the useful lives of the assets, which the Company believes is materially consistent with the pattern of economic benefit provided by the assets.


		December 31,
(U.S. Dollars, in thousands)	Weighted Average Amortization Period	2023			2022
Cost
Developed technology	7.9 years	$	92,416		$	43,699
Patents	10.0 years		43,262			40,108
IPR&D	Indefinite		4,674			300
Customer relationships	12.1 years		49,197			15,572
License and other	9.6 years		24,584			23,295
Trademarks—finite lived	10.0 years		1,797			1,875
	9.5 years		215,930			124,849
Accumulated amortization
Developed technology		$	(28,898	)	$	(17,830	)
Patents			(40,494	)		(37,506	)
Customer relationships			(11,988	)		(6,938	)
License and other			(16,240	)		(14,386	)
Trademarks—finite lived			(820	)		(801	)
			(98,440	)		(77,461	)
Intangible assets, net		$	117,490		$	47,388

Acquired IPR&D represents the fair value assigned to acquired research and development assets that have not reached technological feasibility. In a business combination, the fair value assigned to acquired IPR&D is determined by estimating the remaining costs to develop the acquired technology into commercially viable products, estimating the resulting revenues from the projects, and

discounting the net cash flows to present value. The revenue and cost projections used to value acquired IPR&D are, as applicable, reduced based on the probability of success of developing the asset. Additionally, estimated revenues consider the relevant market sizes and growth factors, expected trends in technology, and the nature and expected timing of new product introductions by the Company and its competitors. The rates utilized to discount the net cash flows to their present value are commensurate with the stage of development of the project and uncertainties in the economic estimates used in the projections. Any future costs to further develop the IPR&D subsequent to acquisition are recorded to research and development expense as incurred.

IPR&D assets are considered to be indefinite-lived assets until the completion or abandonment of the associated research and development efforts. During the period the assets are considered indefinite-lived, they are not amortized but tested for impairment. Impairment testing is performed at least annually or when a triggering event occurs that could indicate a potential impairment. If and when development is complete, which generally occurs when regulatory approval to market a product is obtained, the associated assets are reclassified to developed technology and are amortized over an assigned useful life that best reflects the economic benefits provided by these assets.

Amortization expense for intangible assets was $18.9 million, $9.4 million, and $9.4 million for the years ended December 31, 2023, December 31, 2022, and 2021, respectively. Future amortization expense for intangible assets is estimated as follows:


(U.S. Dollars, in thousands)	Amortization
2024	$	20,948
2025		19,849
2026		18,810
2027		18,426
2028		14,890
Thereafter		19,893
Total finite-lived intangible assets, net	$	112,816
Indefinite-lived intangible assets, net		4,674
Intangible assets, net	$	117,490