Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	$ 734,758	$ 558,699	$ 1,248,595	$ 1,058,750
Alternative Revenue Programs	3,026	11,056	8,943	16,612
Derivative Financial Instruments	(7,834)	60,184	21,894	79,939
Total Revenues	729,950	629,939	1,279,432	1,155,301
All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	0	0	0	0
Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(100,304)	(97,192)	(195,934)	(184,858)
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	(100,304)	(97,192)	(195,934)	(184,858)
Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	319,792	204,430	538,924	438,694
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	(7,834)	60,184	21,894	79,939
Total Revenues	311,958	264,614	560,818	518,633
Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	109,573	108,020	216,186	202,433
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	109,573	108,020	216,186	202,433
Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	65,030	63,993	126,161	126,581
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	65,030	63,993	126,161	126,581
Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	340,667	279,448	563,258	475,900
Alternative Revenue Programs	3,026	11,056	8,943	16,612
Derivative Financial Instruments	0	0	0	0
Total Revenues	343,693	290,504	572,201	492,512
Production of Natural Gas
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	318,404	203,198	535,863	435,859
Production of Natural Gas | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Natural Gas | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Natural Gas | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	318,404	203,198	535,863	435,859
Production of Natural Gas | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Natural Gas | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Natural Gas | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Crude Oil
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	393	524	907	1,211
Production of Crude Oil | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Crude Oil | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Crude Oil | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	393	524	907	1,211
Production of Crude Oil | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Crude Oil | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Production of Crude Oil | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Processing
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	338	303	613	570
Natural Gas Processing | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Processing | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Processing | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	338	303	613	570
Natural Gas Processing | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Processing | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Processing | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Gathering Service
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	3,233	3,917	6,681	8,513
Natural Gas Gathering Service | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Gathering Service | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(61,797)	(60,076)	(119,480)	(118,068)
Natural Gas Gathering Service | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Gathering Service | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Gathering Service | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	65,030	63,993	126,161	126,581
Natural Gas Gathering Service | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Transportation Service
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	100,199	93,262	181,143	173,803
Natural Gas Transportation Service | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Transportation Service | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(27,538)	(25,852)	(54,719)	(46,214)
Natural Gas Transportation Service | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Transportation Service | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	82,481	81,273	163,686	152,891
Natural Gas Transportation Service | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Transportation Service | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	45,256	37,841	72,176	67,126
Natural Gas Storage Service
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	14,597	14,319	29,086	26,551
Natural Gas Storage Service | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Storage Service | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(10,691)	(11,024)	(21,195)	(20,084)
Natural Gas Storage Service | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Storage Service | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	25,288	25,343	50,281	46,635
Natural Gas Storage Service | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Storage Service | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Residential Sales
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	257,100	210,392	413,450	356,938
Natural Gas Residential Sales | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Residential Sales | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Residential Sales | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Residential Sales | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Residential Sales | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Residential Sales | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	257,100	210,392	413,450	356,938
Natural Gas Commercial Sales
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	39,602	30,815	61,845	51,096
Natural Gas Commercial Sales | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Commercial Sales | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Commercial Sales | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Commercial Sales | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Commercial Sales | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Commercial Sales | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	39,602	30,815	61,845	51,096
Natural Gas Industrial Sales
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	1,935	1,279	3,272	2,185
Natural Gas Industrial Sales | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Industrial Sales | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(2)	(2)	(3)	(3)
Natural Gas Industrial Sales | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Industrial Sales | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Industrial Sales | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Natural Gas Industrial Sales | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	1,937	1,281	3,275	2,188
Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(1,043)	690	15,735	2,024
Other | All Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Other | Corporate and Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	(276)	(238)	(537)	(489)
Other | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	657	405	1,541	1,054
Other | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	1,804	1,404	2,219	2,907
Other | Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	0	0	0	0
Other | Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	$ (3,228)	$ (881)	$ 12,512	$ (1,448)