COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Thousands	1 Months Ended					3 Months Ended	9 Months Ended	12 Months Ended
	Oct. 31, 2018 mi	Dec. 31, 2017	Sep. 30, 2017 item	Mar. 31, 2016 mi	May 31, 2007 entity mi	Mar. 31, 2021 USD ($) defendant item	Sep. 30, 2020 item	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Asset retirement obligations						$ 285,401		$ 283,163	$ 263,445	$ 210,323
Number of groundwater extraction wells | item			2
Contingency loss						0
Lease liabilities						$ 443,843		$ 442,737	$ 435,080
Parent Company [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage		15.00%						15.00%
Texas Brine [Member]
Loss Contingencies [Line Items]
Number of defendants | defendant						3
New York Water District Cases [Member]
Loss Contingencies [Line Items]
Number of cases | item						27
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	9			8
Texas Brine and Occidental Chemical Co [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage								20.00%
Occidental Chemical Co [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage		50.00%						30.00%
Texas Brine [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage		35.00%						55.00%
Number of cases | item						2
LADWP [Member]
Loss Contingencies [Line Items]
Number of planned new treatment capabilities | item							2
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						$ 56,335