Property, Plant and Equipment

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, Plant and Equipment:

Property, plant and equipment, at cost, consist of the following at December 31, 2019 and 2018 (in thousands):

	Useful Lives (Years)	December 31,
		2019		2018
Land	—	$	116,728	$	123,518
Land improvements	10 – 30	83,256		63,349
Buildings and improvements	10 – 50	337,728		251,980
Machinery and equipment(a)	2 – 45	3,355,519		2,780,478
Mineral rights and reserves	7 – 60	1,764,067		696,033
Construction in progress	—	1,160,545		883,705
Total		$	6,817,843	$	4,799,063

(a) Consists primarily of (1) short-lived production equipment components, office and building equipment and other equipment with estimated lives ranging 2 – 7 years, (2) production process equipment (intermediate components) with estimated lives ranging 8 – 19 years, (3) production process equipment (major unit components) with estimated lives ranging 20 – 29 years, and (4) production process equipment (infrastructure and other) with estimated lives ranging 30 – 45 years.

The cost of property, plant and equipment is depreciated generally by the straight-line method. Depletion of mineral rights is based on the units-of-production method. Depreciation expense, including depletion, amounted to $183.3 million, $170.0 million and $169.5 million during the years ended December 31, 2019, 2018 and 2017, respectively. Interest capitalized on significant capital projects in 2019, 2018 and 2017 was $30.2 million, $19.3 million and $7.4 million, respectively.