Patents and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2016

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Patents and Other Intangible Assets

	December 31,
(U.S. Dollars, in thousands)	2016			2015
Cost
Patents	$	38,348		$	36,847
License and other		7,611			5,357
Trademarks—finite lived		319			120
		46,278			42,324
Accumulated amortization
Patents		(34,717	)		(33,297	)
License and other		(3,962	)		(3,605	)
Trademarks—finite lived		(138	)		(120	)
		(38,817	)		(37,022	)
	$	7,461		$	5,302

Schedule of Future Amortization Expense

Future amortization expense for intangible assets is estimated as follows:

(U.S. Dollars, in thousands)	Amortization
2017	$	1,524
2018		886
2019		736
2020		785
2021		743
Thereafter		2,787
	$	7,461