COMMITMENTS AND CONTINGENCIES (Narrative) (Details)	1 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	May 31, 2007 entity mi	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Expenditures under the noncapital purchase commitments			$ 40,526,000	$ 60,591,000	$ 76,178,000
Commitments of minimum royalties under mineral leases	$ 211,432,000		211,432,000
Expenditures for mineral royalties under mineral leases			67,933,000	62,978,000	58,048,000
Asset Retirement Obligation	218,117,000		218,117,000	223,872,000	226,594,000
Unrecognized tax benefits	$ 11,643,000		11,643,000	$ 10,828,000	$ 8,447,000	$ 7,057,000
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
Parent Company [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	15.00%
Property, Plant and Equipment [Member]
Loss Contingencies [Line Items]
Unconditional purchase obligations	$ 134,458,000		134,458,000
Recorded unconditional purchase obligation in 2018	134,458,000		134,458,000
Noncapital [Member]
Loss Contingencies [Line Items]
Unconditional purchase obligations	32,145,000		32,145,000
Recorded unconditional purchase obligation in 2018	10,449,000		10,449,000
Ship Construction [Member] | Property, Plant and Equipment [Member]
Loss Contingencies [Line Items]
Recorded unconditional purchase obligation in 2018	$ 68,951,000		68,951,000
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%
Maximum [Member] | EPA [Member]
Loss Contingencies [Line Items]
Estimated implementation costs			1,380,000,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Outstanding standby letters of credit	$ 43,239,000		43,239,000
Hewitt Landfill Matter [Member]
Loss Contingencies [Line Items]
Increase in accrual of liability for claims and litigation			$ 15,239,000