Property, plant and equipment (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of Useful Lives of Assets

The useful lives of these assets are generally 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)	2019			2018
Cost
Buildings	$	3,731		$	3,746
Plant and equipment		46,470			45,744
Instrumentation		82,327			75,542
Computer software		49,696			47,322
Furniture and fixtures		7,328			6,599
Construction in progress		2,201			2,909
Finance lease assets		21,179			—
Property, plant, and equipment, gross		212,932			181,862
Accumulated depreciation		(150,205	)		(139,027	)
Property, plant, and equipment, net	$	62,727		$	42,835