Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	$ 558,699	$ 733,228	$ 1,058,750	$ 1,548,126
Alternative Revenue Programs	11,056	2,801	16,612	5,923
Derivative Financial Instruments	60,184	(18,768)	79,939	(177,930)
Total Revenues	629,939	717,261	1,155,301	1,376,119
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	(97,192)	(86,491)	(184,858)	(170,355)
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	(97,192)	(86,491)	(184,858)	(170,355)
Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	204,430	263,320	438,694	699,455
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	60,184	(18,768)	79,939	(177,930)
Total Revenues	264,614	244,552	518,633	521,525
Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	108,020	95,103	202,433	192,759
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	108,020	95,103	202,433	192,759
Gathering | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	63,993	56,981	126,581	113,394
Alternative Revenue Programs	0	0	0	0
Derivative Financial Instruments	0	0	0	0
Total Revenues	63,993	56,981	126,581	113,394
Utility | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	279,448	404,315	475,900	712,873
Alternative Revenue Programs	11,056	2,801	16,612	5,923
Derivative Financial Instruments	0	0	0	0
Total Revenues	290,504	407,116	492,512	718,796
Production of Natural Gas
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	203,198	259,770	435,859	692,129
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	203,198	259,770	435,859	692,129
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	524	526	1,211	1,154
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	524	526	1,211	1,154
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	303	209	570	583
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	303	209	570	583
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	3,917	1,728	8,513	4,374
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	(60,076)	(55,253)	(118,068)	(109,020)
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	63,993	56,981	126,581	113,394
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	93,262	87,839	173,803	171,602
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	(25,852)	(21,751)	(46,214)	(42,568)
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	81,273	73,794	152,891	149,996
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	37,841	35,796	67,126	64,174
Natural Gas Storage Service
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	14,319	12,251	26,551	24,541
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	(11,024)	(9,219)	(20,084)	(18,215)
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	25,343	21,470	46,635	42,756
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	210,392	318,649	356,938	562,955
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	210,392	318,649	356,938	562,955
Natural Gas Commercial Sales
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	30,815	48,966	51,096	83,461
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	30,815	48,966	51,096	83,461
Natural Gas Industrial Sales
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	1,279	2,764	2,185	4,403
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)	(4)	(3)	(4)
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	1,281	2,768	2,188	4,407
Other
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	690	526	2,024	2,924
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	(238)	(264)	(489)	(548)
Other | Exploration and Production | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	405	2,815	1,054	5,589
Other | Pipeline and Storage | Total Reportable Segments
Disaggregation of Revenue [Line Items]
Total Revenues from Contracts with Customers	1,404	(161)	2,907	7
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	$ (881)	$ (1,864)	$ (1,448)	$ (2,124)