Capitalization (Narrative) (Details) $ / shares in Units, $ in Thousands				6 Months Ended
	Mar. 06, 2025 USD ($)	Feb. 28, 2025 USD ($)	Feb. 19, 2025 USD ($)	Mar. 31, 2025 USD ($) $ / shares shares	Mar. 31, 2024 USD ($)	Jan. 31, 2025 USD ($)	Jan. 30, 2025 bank	Sep. 30, 2024 USD ($)	Apr. 30, 2024 USD ($)	Mar. 08, 2024 USD ($)	Feb. 14, 2024 USD ($) lender	Sep. 30, 2023 USD ($)
Debt Instrument [Line Items]
Stock repurchase program, authorized amount										$ 200,000
Share repurchases (in shares) | shares				608,295
Current Portion of Long-Term Debt				$ 350,000				$ 500,000
Cash Held in Trust for Bondholders				51,352	$ 0			0				$ 0
Repayments of long-term debt				954,086	0
Net Proceeds from Issuance of Long-Term Debt				989,019	0
Premiums Paid on Early Redemption of Debt				(2,385)	$ 0
Unamortized Debt Expense				7,166				5,604
5.50% Notes Due March 15, 2030
Debt Instrument [Line Items]
Long-term debt, interest rate	5.50%		5.50%
Long-term debt, face amount			$ 500,000
Net Proceeds from Issuance of Long-Term Debt			$ 495,400
Percentage of principal amount			101.00%
Maximum interest rate adjustment			2.00%
5.50% Notes Due March 15, 2030 | Maximum
Debt Instrument [Line Items]
Long-term debt, interest rate			7.50%
5.95% Notes Due March 15, 2035
Debt Instrument [Line Items]
Long-term debt, interest rate			5.95%
Long-term debt, face amount			$ 500,000
Net Proceeds from Issuance of Long-Term Debt			$ 493,600
Percentage of principal amount			101.00%
Maximum interest rate adjustment			2.00%
5.95% Notes Due March 15, 2035 | Maximum
Debt Instrument [Line Items]
Long-term debt, interest rate			7.95%
5.50% Notes Due January 2026
Debt Instrument [Line Items]
Long-term debt, interest rate	5.50%
Long-term debt, face amount	$ 500,000
Debt instrument redeemed	503,300
5.50% Notes Due January 2026 | Exploration and Production and Gathering
Debt Instrument [Line Items]
Premiums Paid on Early Redemption of Debt	1,800
5.50% Notes Due January 2026 | Pipeline and Storage
Debt Instrument [Line Items]
Unamortized Debt Expense	1,500
Indenture From 1974
Debt Instrument [Line Items]
Cash Held in Trust for Bondholders						$ 53,200
Carrying amount of long-term debt				$ 50,000
Long term debt, interest payments remaining, value						$ 3,200
Interest payment		$ 1,800
Share Repurchase Plan
Debt Instrument [Line Items]
Share repurchases (in shares) | shares				774,768
Share repurchase program, average cost per share (in dollars per share) | $ / shares				$ 63.74
Share repurchases				$ 49,800
Credit Agreement
Debt Instrument [Line Items]
Number of banks In syndicate | bank							11
Maximum borrowing capacity				1,000,000
Extended term of credit agreement							1 year
7.38% Notes Due June 2025
Debt Instrument [Line Items]
Current Portion of Long-Term Debt				$ 50,000				$ 50,000
Long-term debt, interest rate				7.38%				7.38%
7.38% Notes Due June 2025 | Principal
Debt Instrument [Line Items]
Cash Held in Trust for Bondholders				$ 50,000
5.20% Notes Due July 2025
Debt Instrument [Line Items]
Current Portion of Long-Term Debt	$ 450,000							$ 450,000
Long-term debt, interest rate	5.20%							5.20%
Long-term debt, face amount	$ 450,000
Debt instrument redeemed	450,800
5.20% Notes Due July 2025 | Exploration and Production and Gathering
Debt Instrument [Line Items]
Premiums Paid on Early Redemption of Debt	600
5.20% Notes Due July 2025 | Pipeline and Storage
Debt Instrument [Line Items]
Unamortized Debt Expense	$ 200
Term Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity				300,000							$ 300,000
Long-term debt, face amount									$ 300,000
Number of lenders | lender											6
Proceeds from debt, net of issuance costs				$ 299,400
Rate adjustment to SOFR				0.0010
Spread on variable rate				1.375%
Term Loan Agreement | 5.79% Through May 2025
Debt Instrument [Line Items]
Long-term debt, variable interest rate				5.79%