Property, Plant and Equipment

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment

G.    PROPERTY, PLANT AND EQUIPMENT

Property, plant and equipment, net consisted of the following at December 31, 2021 and 2020:

	2021		2020
	(in thousands)
Land	$	17,207	$	17,207
Buildings		126,468		108,221
Machinery, equipment and software		994,828		956,035
Furniture and fixtures		28,743		28,487
Leasehold improvements		64,110		61,276
Construction in progress		8,105		13,098
		1,239,461		1,184,324
Less: accumulated depreciation		852,221		789,524
	$	387,240	$	394,800

Depreciation of property, plant and equipment for the years ended December 31, 2021, 2020, and 2019 was $91.1 million, $80.1 million, and $70.8 million, respectively. As of December 31, 2021 and 2020, the gross book value included in machinery and equipment for internally manufactured test systems being leased by customers was $13.4 million and $23.4 million, respectively. As of December 31, 2021 and 2020, the accumulated depreciation on these test systems was $8.7 million and $7.5 million, respectively.