Patents and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Patents and Other Intangible Assets

	December 31,
(U.S. Dollars, in thousands)	2017			2016
Cost
Patents	$	38,621		$	38,348
License and other		10,276			7,611
Trademarks—finite lived		533			319
		49,430			46,278
Accumulated amortization
Patents		(34,151	)		(34,717	)
License and other		(4,625	)		(3,962	)
Trademarks—finite lived		(193	)		(138	)
		(38,969	)		(38,817	)
Patents and other intangible assets, net	$	10,461		$	7,461

Schedule of Future Amortization Expense

Future amortization expense for intangible assets is estimated as follows:

(U.S. Dollars, in thousands)	Amortization
2018	$	2,352
2019		1,909
2020		1,366
2021		1,321
2022		1,314
Thereafter		2,199
Total	$	10,461