COMMITMENTS AND CONTINGENCIES (Narrative) (Details)	1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 item	Mar. 31, 2016 mi	May 31, 2007 entity mi	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 218,117,000				$ 223,953,000	$ 215,421,000	$ 218,117,000	$ 214,709,000	$ 226,012,000	$ 223,872,000
Number of groundwater extraction wells | item		2
Parent Company [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	15.00%
Cooperating Parties Group [Member]
Loss Contingencies [Line Items]
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
Number of miles for bank-to-bank dredging remedy | mi			8
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						$ 45,067,000
Hewitt Landfill Matter [Member]
Loss Contingencies [Line Items]
Increase in accrual of liability for claims and litigation					$ 14,216,000		$ 15,239,000