Property, plant and equipment (Tables)

12 Months Ended

Dec. 31, 2014

Property Plant And Equipment [Abstract]

Schedule of Property Plant and Equipment

	December 31,
(U.S. Dollars in thousands)	2014			2013
Cost
Buildings	$	3,683		$	4,075
Plant, equipment and instrumentation		140,110			133,427
Furniture and fixtures		5,779			5,872
		149,572			143,374
Accumulated depreciation		(101,023	)		(89,002	)
	$	48,549		$	54,372