COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended			24 Months Ended
	Dec. 31, 2017 USD ($)	May 31, 2007 entity mi	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Expenditures under the noncapital purchase commitments				$ 56,674	$ 40,526	$ 60,591
Commitments of minimum royalties under mineral leases			$ 240,575	240,575			$ 240,575
Expenditures for mineral royalties under mineral leases				76,761	67,933	62,978
Asset Retirement Obligation	$ 218,117		225,726	225,726	218,117	223,872	225,726
Unrecognized tax benefits	$ 11,643		3,661	3,661	$ 11,643	$ 10,828	3,661	$ 8,447
Number of other companies to perform a Remedial Investigation/ Feasibility Study related to the Lower Passaic River Clean-Up lawsuit | entity		70
Number of miles of the River used in the Remedial Investigation/Feasibility Study | mi		17
Increase in accrual of liability for claims and litigation							34,271
Property, Plant and Equipment [Member]
Loss Contingencies [Line Items]
Unconditional purchase obligations			35,248	35,248			35,248
Recorded unconditional purchase obligation in 2018			35,248	35,248			35,248
Noncapital [Member]
Loss Contingencies [Line Items]
Unconditional purchase obligations			36,722	36,722			36,722
Recorded unconditional purchase obligation in 2018			11,912	$ 11,912			11,912
Parent Company [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	15.00%
New York Water District Cases [Member]
Loss Contingencies [Line Items]
Number of cases | item				11
NAFTA Arbitration [Member]
Loss Contingencies [Line Items]
Contingency loss				$ 0
Occidental Chemical Co [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	50.00%
Texas Brine [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	35.00%
Number of cases | item				2
Minimum [Member] | NAFTA Arbitration [Member]
Loss Contingencies [Line Items]
Arbitration period				2 years
Maximum [Member] | EPA [Member]
Loss Contingencies [Line Items]
Estimated implementation costs				$ 1,380,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Outstanding standby letters of credit			44,979	44,979			$ 44,979
Hewitt Landfill Matter [Member]
Loss Contingencies [Line Items]
Increase in accrual of liability for claims and litigation			$ 10,392	$ 19,032