Property, plant and equipment (Tables)

12 Months Ended

Dec. 31, 2015

Property Plant And Equipment [Abstract]

Schedule of Property Plant and Equipment

	December 31,
(U.S. Dollars in thousands)	2015			2014
Cost
Buildings	$	3,328		$	3,683
Plant, equipment and instrumentation		150,366			140,110
Furniture and fixtures		5,711			5,779
		159,405			149,572
Accumulated depreciation		(107,099	)		(101,023	)
	$	52,306		$	48,549