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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) - USD ($) | 1 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Mar. 31, 2021 | Mar. 31, 2020 | Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Reserve for expected credit losses |  |  | $ 10,607,000 | $ 951,000 |
Loans receivable in other current assets |  |  | 14,300,000 |  | $ 13,700,000
Loans receivable in other noncurrent assets |  |  | 33,900,000 |  | $ 35,300,000
Proceeds from sale leaseback transaction |  |  | 0 | 4,000,000 |
Proceeds from sale leaseback transaction - solar | $ 12,100,000 |  | 12,124,000 | $ 0 |
Clean Energy Ventures |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Reserve for expected credit losses |  |  | 5,200,000 |  |
Natural Gas Distribution |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Proceeds from sale leaseback transaction |  | $ 4,000,000.0 | $ 0 |  |
Minimum |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Loans receivable, term |  |  | 2 years |  |
Maximum |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Loans receivable, term |  |  | 10 years |  |

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