Patents and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2012

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Patents and Other Intangible Assets

	December 31,
(U.S. Dollars, in thousands)	2012			2011
	(Restated)			(Restated)
Cost
Patents	$	38,905		$	38,893
Trademarks—definite lived		657			545
		39,562			39,438
Accumulated amortization
Patents		(31,845	)		(30,211	)
Trademarks—definite lived		(427	)		(381	)
		(32,272	)		(30,592	)
Patents and other intangible assets, net	$	7,290		$	8,846