PROPERTY, PLANT & EQUIPMENT (Property, Plant and Equipment) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total, gross		$ 7,969,312	$ 7,185,818
Less allowances for depreciation, depletion and amortization		4,050,381	3,924,380
Total, net		3,918,931	3,261,438
Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Total, gross	[1]	2,742,285	2,374,051
Buildings [Member]
Property, Plant and Equipment [Line Items]
Total, gross		135,655	127,369
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total, gross		4,740,212	4,316,243
Leaseholds [Member]
Property, Plant and Equipment [Line Items]
Total, gross		17,354	17,595
Deferred Asset Retirement Costs [Member]
Property, Plant and Equipment [Line Items]
Total, gross		172,631	168,258
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total, gross		161,175	182,302
Depletable Land [Member]
Property, Plant and Equipment [Line Items]
Total, gross		$ 1,606,303	$ 1,327,402

[1] Includes depletable land, as follows: December 31, 2017 - $1,606,303 thousand and December 31, 2016 - $1,327,402 thousand.