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COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) site	Sep. 30, 2018 USD ($)
Site Contingency [Line Items]
Number of MGP sites \| site		5
Recovery from third party of environmental remediation cost, period		7 years
Regulatory assets		$ 370,024	$ 368,592
Manufactured gas plant remediation		129,556	130,800
Minimum
Site Contingency [Line Items]
Product liability contingency, loss exposure in excess of accrual, best estimate		117,700
Maximum
Site Contingency [Line Items]
Product liability contingency, loss exposure in excess of accrual, best estimate		204,100
Expended, net of recoveries
Site Contingency [Line Items]
Regulatory assets		$ 32,764	33,017
RAC
Site Contingency [Line Items]
Public utilities, approved rate, amount	$ 9,400		$ 7,000