Property, Plant and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property, Plant and Equipment, Net

December 31

(add 000)	2017			2016
Land and land improvements	$	974,622		$	915,158
Mineral reserves and interests		1,162,289			1,114,560
Buildings		154,564			151,115
Machinery and equipment		4,006,619			3,766,975
Construction in progress		199,973			167,722
		6,498,067			6,115,530
Less accumulated depreciation, depletion and amortization		(2,905,254	)		(2,692,135	)
Total	$	3,592,813		$	3,423,395

Gross Asset Value and Accumulated Amortization for Machinery and Equipment Recorded under Capital Lease

The gross asset value and accumulated amortization for machinery and equipment recorded under capital leases at December 31 were as follows:

(add 000)	2017			2016
Machinery and equipment under capital leases	$	23,919		$	23,117
Less accumulated amortization		(11,243	)		(8,077	)
Total	$	12,676		$	15,040