Debt (Narrative) (Details)	3 Months Ended
	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Less: current portion	$ (414,800,000)	$ (414,400,000)
Debt Instrument, Unamortized Discount (Premium), Net	(500,000)	(600,000)
Short-Term Bank Loans and Notes Payable	150,000,000
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000
Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	220,000,000	140,000,000
Less: current portion	(200,000)	(200,000)
Deferred Finance Costs, Net, Including Acquisition Adjustments	(6,400,000)	(6,600,000)
Debt Instrument, Unamortized Discount (Premium), Net	(2,200,000)	(2,100,000)
3.95% Senior Notes due 2049 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 425,000,000.0	425,000,000.0
Debt Instrument, Interest Rate, Effective Percentage	3.95%
Revolving Credit Facility [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Debt Covenant, Total Debt to Total Capitalization Ratio, Maximum	0.67
Uncommitted Accordion Feature	$ 150,000,000
3.25% First Mortgage Bonds due 2040 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 140,000,000.0	140,000,000.0
Debt Instrument, Interest Rate, Effective Percentage	3.20%
U.S. Government note maturing in February 2061 - 4.20% [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		16,600,000
Debt instrument interest percentage	4.20%
4.25% Tax-exempt First Mortgage Bonds due 2027 | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 100,000,000.0	100,000,000.0
Debt Instrument, Interest Rate, Effective Percentage	4.25%
4.00% Tax-exempt First Mortgage Bonds due 2027 | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 40,000,000.0	$ 40,000,000.0
Debt Instrument, Interest Rate, Effective Percentage	4.00%