Property, Plant and Equipment

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

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


	As of December 31,
	2020		2019
Property, plant and equipment
Land and buildings	$	58,296	$	57,222
Machinery and equipment	339,268		321,110
Construction in progress	1,270		25,416
Total	398,834		403,748
Less: Accumulated depreciation	175,144		147,771
Property, plant and equipment, net	$	223,690	$	255,977

We monitor property, plant and equipment for any indicators of potential impairment. We recognized impairment charges of $4.1 million, $0.6 million, and $5.2 million for the years ended December 31, 2020, 2019, and 2018, respectively, related to the early retirement of identified fixed assets. The impairment charges were recorded to the “Other operating expense, 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, 2020, 2019, and 2018, we recorded depreciation expense of $31.3 million, $30.4 million, and $28.5 million, respectively.