PROPERTY, PLANT & EQUIPMENT (Property, Plant and Equipment) (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total, gross		$ 8,749,218	$ 8,457,619
Less allowances for depreciation, depletion and amortization		4,433,180	4,220,312
Total, net		4,316,038	4,237,307
Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Total, gross	[1]	2,920,963	2,823,092
Buildings [Member]
Property, Plant and Equipment [Line Items]
Total, gross		141,898	139,948
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total, gross		5,362,279	5,106,918
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total, gross		1,677	18,217
Deferred Asset Retirement Costs [Member]
Property, Plant and Equipment [Line Items]
Total, gross		167,484	183,324
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total, gross		154,917	186,120
Depletable Land [Member]
Property, Plant and Equipment [Line Items]
Total, gross		$ 1,667,642	$ 1,626,899

[1] Includes depletable land: December 31, 2019 — $1,667,642 thousand and December 31, 2018 — $1,626,899 thousand.