Patents and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2018

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Patents and Other Intangible Assets

		December 31,
(U.S. Dollars, in thousands)	Weighted Average Amortization Period	2018			2017
Cost
Patents	10 years	$	39,085		$	38,621
Developed technology	10 years		12,400			—
IPR&D	Indefinite		26,800			—
License and other	7 years		14,654			10,276
Trademarks—finite lived	9 years		840			533
	9 years		93,779			49,430
Accumulated amortization
Patents		$	(35,016	)	$	(34,151	)
Developed technology			(827	)		—
IPR&D			—			—
License and other			(5,744	)		(4,625	)
Trademarks—finite lived			(295	)		(193	)
			(41,882	)		(38,969	)
Patents and other intangible assets, net		$	51,897		$	10,461

Schedule of Future Amortization Expense

Future amortization expense for intangible assets, including IPR&D, is estimated as follows:

(U.S. Dollars, in thousands)	Amortization
2019	$	6,604
2020		6,205
2021		6,146
2022		6,138
2023		5,495
Thereafter		21,309
Total	$	51,897