Property, Plant and Equipment

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment [Abstract]

Property, plant and equipment are comprised of the following amounts:


	As of December 31,
	2021		2020

Land and buildings	$	57,991	$	58,296
Machinery and equipment	344,041		339,268
Construction in progress	5,009		1,270
Total	407,041		398,834
Less: Accumulated depreciation	197,936		175,144
Property, plant and equipment, net	$	209,105	$	223,690

We monitor property, plant and equipment for any indicators of potential impairment. We recognized impairment charges of $4.1 million and $0.6 million for the years ended December 31, 2020 and 2019, respectively, related to the early retirement of identified fixed assets. There were no impairment charges for the year ended December 31, 2021. The impairment charges were recorded to the “Other operating expense (income), net,” line item on the Consolidated Statements of Operations and Comprehensive Income (Loss). The impairment charges were determined by writing the assets down to the estimated salvage value, less disposal costs.

For the years ended December 31, 2021, 2020, and 2019, we recorded depreciation expense of $31.8 million, $31.3 million, and $30.4 million, respectively.