BUSINESS COMBINATION - EGT and ELK Acquisition (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Jul. 01, 2018	Dec. 31, 2017
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Property, Plant and Equipment			$ 1,202,435
Accounts Receivable			45,875
Provision for Uncollectibles			(6,579)
Natural Gas in Storage			12,204
Materials and Supplies			345
Other Prepayments and Current Assets			200
Deferred Income Taxes			39,470
Regulatory Assets			136,212
Goodwill	$ 702,070	$ 734,607	700,286	$ 3,578
Total assets acquired			2,130,448
Accounts Payable			13,089
Other Current Liabilities			9,185
Environmental Remediation Costs - Current			7,100
Pension and Other Postretirement Benefits			3,213
Environmental Remediation Costs - Non Current			66,165
Regulatory Liabilities			192,811
Asset Retirement Obligation			113,093
Other			1,107
Total liabilities assumed			405,763
Total net assets acquired			$ 1,724,685