PROPERTY, PLANT & EQUIPMENT (Property, Plant and Equipment) (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		$ 6,891,287	$ 6,608,842
Less allowances for depreciation, depletion and amortization		3,734,997	3,537,212
Property, plant & equipment, net		3,156,290	3,071,630
Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross	[1]	2,305,801	2,273,874
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		124,950	126,833
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		4,124,808	3,952,423
Leaseholds [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		14,143	13,451
Deferred Asset Retirement Costs [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		166,252	163,644
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		155,333	78,617
Depletable Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant & equipment, gross		$ 1,296,211	$ 1,287,225

[1] Includes depletable land, as follows: December 31, 2015 - $1,296,211 thousand and December 31, 2014 - $1,287,225 thousand.