Property, Plant and Equipment

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

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



	As of December 31,
	2018		2017
Land and buildings	$	69,455	$	54,833
Machinery and equipment	401,729		302,470
Construction in progress	35,122		14,346
Total	506,306		371,649
Less—accumulated depreciation	145,278		112,369
Property, plant and equipment, net	$	361,028	$	259,280

During the year ended December 31, 2018, we acquired $66.0 million in property, plant and equipment with the Paragon Medical, Bridgemedica, and Technical Arts acquisitions. During the year ended December 31, 2017, we acquired $14.0 million in property, plant and equipment with the NN Vandalia acquisition.

We monitor property, plant and equipment for any indicators of potential impairment. During 2018, we recognized an impairment charge of $5.2 million 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 charges for the years ended December 31, 2017 and 2016.

For the years ended December 31, 2018, 2017, and 2016, we recorded depreciation expense of $38.6 million, $28.9 million, and $24.7 million, respectively.