Property, Plant and Equipment

6 Months Ended

Jun. 30, 2019

Property, Plant and Equipment [Abstract]

The components of Property, plant and equipment, net are as follows:



(in thousands)	June 30, 2019		December 31, 2018		June 30, 2018
Land	$	39,241	$	29,739	$	29,579
Land improvements and leasehold improvements	84,127		68,826		68,384
Buildings and storage facilities	327,418		284,998		280,226
Machinery and equipment	514,030		393,640		377,202
Construction in progress	164,532		102,394		37,456
	1,129,348		879,597		792,847
Less: accumulated depreciation	433,521		402,886		384,272
	$	695,827	$	476,711	$	408,575

Depreciation expense on property, plant and equipment was $32.7 million and $23.2 million for the six months ended June 30, 2019 and 2018, respectively. Additionally, depreciation expense on property, plant and equipment was $15.0 million and $11.5 million for the three months ended June 30, 2019 and 2018, respectively.

In the second quarter of 2019, the Company recorded a $3.1 million impairment charge related to its remaining Tennessee facilities in the Trade group. The Company wrote down the value of these assets to the extent their carrying values exceeded their fair value. The Company classified the significant assumptions used to determine the fair value of the impaired assets as Level 3 inputs in the fair value hierarchy.

Rail Group Assets

The components of Rail Group assets leased to others are as follows:



(in thousands)	June 30, 2019		December 31, 2018		June 30, 2018
Rail Group assets leased to others	$	688,320	$	640,349	$	564,555
Less: accumulated depreciation	128,609		118,564		106,131
	$	559,711	$	521,785	$	458,424

Depreciation expense on Rail Group assets leased to others amounted to $13.7 million and $12.2 million for the six months ended June 30, 2019 and 2018, respectively. Additionally, depreciation expense on Rail Group assets leased to others amounted to $7.0 million and $6.0 million for the three months ended June 30, 2019 and 2018, respectively.