LONG-TERM DEBT - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long-term debt	$ 2,706,512	$ 2,896,506
2022 Revolving Credit Agreement \| Commercial Paper
Debt Instrument [Line Items]
Maximum borrowing capacity	500,000
Available borrowing capacity	384,000
Line of Credit \| 2022 Revolving Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	520,000
Swingline sublimit	125,000
Letter of credit sublimit	75,000
Available borrowing capacity	$ 404,000
Minimum
Debt Instrument [Line Items]
Equity to capitalization ratio (ECR) requirement (as a percent)	18.00%
Debt service ratio (DSR) requirement	1.025
Minimum \| All Other Long-Term Debt
Debt Instrument [Line Items]
Debt service ratio (DSR) requirement	1.10
Minimum \| Springerville certificates, Series B, 7.14%, due through 2033 \| Mortgages
Debt Instrument [Line Items]
Debt service ratio (DSR) requirement	1.02

The Debt Service Ratio (DSR) requirement per the terms of long-term debt agreements.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

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