SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - PROPERTY PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Property Classifications
Total property, plant and equipment	$ 3,782,359	$ 3,304,491
Accumulated depreciation and amortization	(741,193)	(653,442)
Property, plant and equipment, net	3,041,166	2,651,049
Utility \| Distribution facilities
Property Classifications
Total property, plant and equipment	$ 2,414,603	2,151,249
Utility \| Distribution facilities \| Minimum
Property Classifications
Estimated Useful Lives	38 years
Utility \| Distribution facilities \| Maximum
Property Classifications
Estimated Useful Lives	74 years
Utility \| Transmission facilities
Property Classifications
Total property, plant and equipment	$ 330,912	295,692
Utility \| Transmission facilities \| Minimum
Property Classifications
Estimated Useful Lives	35 years
Utility \| Transmission facilities \| Maximum
Property Classifications
Estimated Useful Lives	56 years
Utility \| Storage facilities
Property Classifications
Total property, plant and equipment	$ 79,916	79,470
Utility \| Storage facilities \| Minimum
Property Classifications
Estimated Useful Lives	34 years
Utility \| Storage facilities \| Maximum
Property Classifications
Estimated Useful Lives	47 years
Nonutility \| Solar property
Property Classifications
Total property, plant and equipment	$ 879,597	720,562
Nonutility \| Solar property \| Minimum
Property Classifications
Estimated Useful Lives	15 years
Nonutility \| Solar property \| Maximum
Property Classifications
Estimated Useful Lives	25 years
Nonutility \| Midstream property
Property Classifications
Estimated Useful Lives	30 years
Total property, plant and equipment	$ 28,445	6,747
Nonutility \| All other property
Property Classifications
Total property, plant and equipment	$ 48,886	$ 50,771
Nonutility \| All other property \| Minimum
Property Classifications
Estimated Useful Lives	5 years
Nonutility \| All other property \| Maximum
Property Classifications
Estimated Useful Lives	35 years

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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