SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) state item segment factor	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2016 USD ($)
Accounting Policies [Line Items]
Number of states | state	20
Number of demographic factors | factor	3
Restructuring charges	$ 4,988	$ 1,308	$ 1,509
Bad debt expense	1,450	2,031	602
Write-offs of accounts receivables	1,483	2,561	1,946
Capitalized software costs	7,003	8,753
Capitalized software costs during the year	$ 1,482	921	1,695
Number of Rabbi Trusts established | item	2
Net gains of the Rabbi Trust investments	$ (1,517)	1,169	4,398
Unrealized net gains (losses) of the Rabbi Trust investments	(1,769)	(1,049)	4,234
Losses on impairment of long-lived assets	5,190	3,095	0
Assets subject to fair value measurement on a nonrecurring basis	0	2,172
Goodwill	$ 3,094,824	$ 3,094,824	3,081,521	$ 3,086,716
Percentage of goodwill in total assets	37.00%	38.00%
Number of operating segments | segment	4
Number of reporting units | item	18
Percentage of net property, plant & equipment in total assets	38.00%
Percentage of net other intangible assets in total assets	9.00%
Number of Facilities | item	8
Proceeds from sale of future production			153,282	$ 73,644
Amortization term of proceeds from sale of future production	25 years
Stripping costs	$ 50,409	$ 44,896	41,716
Capitalized pre-production stripping costs	61,369	44,035
Excess tax benefits from share-based compensation	18,376	3,464	161
Carrying value of reclamation obligations	226,594	226,565	$ 228,234
Spread between the amount accrued and the maximum environmental loss	3,154
Maximum self-insurance coverage per occurrence for losses related to workers' compensation	2,000
Maximum self-insurance coverage per occurrence for automotive and general/product liability	$ 3,000
Accounting Standards Codification Topic 740 - Income Taxes recognition threshold for uncertain tax positions	50.00%
LIFO method used for percentage of inventory	67.00%
Debt Issuance Cost		$ 20,805
Goodwill [Member]
Accounting Policies [Line Items]
Number of reporting units | item	9
Minimum [Member] | Machinery and Equipment [Member]
Accounting Policies [Line Items]
Estimated service lives	3 years
Minimum [Member] | Buildings [Member]
Accounting Policies [Line Items]
Estimated service lives	7 years
Minimum [Member] | Land Improvements [Member]
Accounting Policies [Line Items]
Estimated service lives	8 years
Maximum [Member] | Machinery and Equipment [Member]
Accounting Policies [Line Items]
Estimated service lives	25 years
Maximum [Member] | Buildings [Member]
Accounting Policies [Line Items]
Estimated service lives	20 years
Maximum [Member] | Land Improvements [Member]
Accounting Policies [Line Items]
Estimated service lives	20 years
Scenario, Forecast [Member]
Accounting Policies [Line Items]
Estimated deferred revenue to be recognized in the next 12 months					$ 6,400