Intangible assets (Tables)

12 Months Ended

Dec. 31, 2020

Goodwill And Intangible Assets Disclosure [Abstract]

Intangible assets are recorded at cost, or when acquired as a part of a business combination, at estimated fair value. 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 these assets.

		December 31,
(U.S. Dollars, in thousands)	Weighted Average Amortization Period	2020			2019
Cost
Patents	10 years	$	50,326		$	42,034
Developed technology	10 years		44,334			39,200
IPR&D	Indefinite		300			—
Customer relationships	7 years		15,685			7,430
License and other	8 years		16,941			15,960
Trademarks—finite lived	10 years		1,812			942
	9 years		129,398			105,566
Accumulated amortization
Patents		$	(46,272	)	$	(38,246	)
Developed technology			(8,925	)		(4,523	)
Customer relationships			(2,095	)		(535	)
License and other			(11,006	)		(7,701	)
Trademarks—finite lived			(583	)		(422	)
			(68,881	)		(51,427	)
Intangible assets, net		$	60,517		$	54,139

Schedule of Future Amortization Expense

Future amortization expense for intangible assets is estimated as follows:

(U.S. Dollars, in thousands)	Amortization
2021	$	9,292
2022		9,143
2023		8,488
2024		8,020
2025		7,001
Thereafter		18,273
Total finite-lived intangible assets, net	$	60,217
Indefinite-lived intangible assets, net		300
Intangible assets, net	$	60,517