Property, plant and equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Schedule of Useful Lives of Assets

The useful lives of these assets are as follows:

	Years
Buildings	25 to 33
Plant and equipment	1 to 10
Instrumentation	3 to 4
Computer software	3 to 7
Furniture and fixtures	4 to 8

Schedule of Property, Plant and Equipment

The assets and related accumulated depreciation are adjusted for property retirements and disposals, with the resulting gain or loss included in earnings. Fully depreciated assets remain in the accounts until retired from service.

	December 31,
(U.S. Dollars, in thousands)	2018			2017
Cost
Buildings	$	3,746		$	3,725
Plant and equipment		45,744			47,588
Instrumentation		75,542			75,818
Computer software		47,322			48,604
Furniture and fixtures		6,599			7,605
Construction in progress		2,909			769
		181,862			184,109
Accumulated depreciation		(139,027	)		(138,970	)
Property, plant and equipment, net	$	42,835		$	45,139