Property, Plant and Equipment

12 Months Ended

Dec. 31, 2016

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, 2016 and 2015 (in thousands):

	Useful Lives (Years)	December 31,
		2016		2015
Land	—	$	120,842	$	120,702
Land improvements	5 – 30	59,387		57,833
Buildings and improvements	10 – 45	256,603		236,577
Machinery and equipment(a)	2 – 45	2,501,481		2,216,085
Long-term mineral rights and production equipment costs	7 – 60	654,006		652,871
Construction in progress	—	318,203		416,404
Total(b)		$	3,910,522	$	3,700,472

(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.

(b) As of December 31, 2015, $424.1 million of Property, plant and equipment, at cost, was classified as Assets held for sale in the consolidated balance sheets. See Note 3, “Divestitures,” for additional information.

The cost of property, plant and equipment is depreciated generally by the straight-line method. Depletion of long-term mineral rights is based on the units-of-production method. Depreciation expense amounted to $178.8 million, $162.2 million and $97.9 million during the years ended December 31, 2016, 2015 and 2014, respectively. Depreciation expense related to discontinued operations was $8.9 million, $18.5 million and $2.3 million during the years ended December 31, 2016, 2015 and 2014, respectively. Interest capitalized on significant capital projects in 2016, 2015 and 2014 was $6.8 million, $11.2 million and $2.4 million, respectively.