Property, Plant and Equipment

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

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



	As of December 31,
	2019		2018
Property, plant and equipment
Land and buildings	$	80,647	$	69,455
Machinery and equipment	433,016		401,729
Construction in progress	38,829		35,122
Total	552,492		506,306
Less: Accumulated depreciation	177,979		145,278
Property, plant and equipment, net	$	374,513	$	361,028

We monitor property, plant and equipment for any indicators of potential impairment. We recognized an impairment charge of $0.6 million and $5.2 million for the years ended December 31, 2019 and 2018, respectively, related to the early retirement of identified fixed assets. The impairment charge was recorded to the “Other operating (income) expense, net,” line item on the Consolidated Statements of Operations and Comprehensive Income (Loss). The impairment charge was determined by writing the assets down to the estimated salvage value, less disposal costs. We recorded no impairment charge for the year ended December 31, 2017.

For the years ended December 31, 2019, 2018, and 2017, we recorded depreciation expense of $44.8 million, $38.6 million, and $28.9 million, respectively.