Business Segment Information - Information By Segment (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2024		Sep. 30, 2023		Sep. 30, 2022
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	$ 1,944,810	[2]	$ 2,173,771	[3]	$ 2,186,046
Intersegment Revenues		0		0		0
Interest Income		8,727		11,479		6,111
Interest Expense		138,695		131,886		130,357
Depreciation, Depletion and Amortization		457,026		409,573		369,790
Significant Non-Cash Item: Impairment of Assets		519,129		0		0
Income Tax Expense (Benefit)		9,742		164,533		116,629
Significant Item: Gain on Sale of Assets		0		0		12,736
Segment Profit: Net Income (Loss)		77,513		476,866		566,021
Expenditures for Additions to Long-Lived Assets		942,015		1,123,573		829,388
Segment Assets		8,319,770		8,280,260		7,896,262
Operating Revenues		1,944,810		2,173,771		2,186,046
Total Reportable Segments
Segment Reporting Information [Line Items]
Operating Revenues		2,315,058		2,510,323		2,500,572
All Other
Segment Reporting Information [Line Items]
Operating Revenues		0		0		6
Corporate
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	0	[2]	0	[3]	165
Corporate and Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment Revenues		(370,248)		(336,552)		(314,697)
Interest Income		(8,703)		(5,662)		(1,024)
Interest Expense		(17,839)		(15,309)		(6,143)
Depreciation, Depletion and Amortization		473		429		183
Significant Non-Cash Item: Impairment of Assets		0
Income Tax Expense (Benefit)		145		(983)		(4,429)
Significant Item: Gain on Sale of Assets						0
Segment Profit: Net Income (Loss)		(1,588)		(3,498)		(12,650)
Expenditures for Additions to Long-Lived Assets		970		754		1,212
Segment Assets		(163,332)		(126,633)		(186,281)
Operating Revenues		(370,248)		(336,552)		(314,532)
Total Reportable Segments | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	1,944,810	[2]	2,173,771	[3]	2,185,881
Intersegment Revenues		370,248		336,552		314,691
Interest Income		17,430		17,141		7,132
Interest Expense		156,160		147,038		136,496
Depreciation, Depletion and Amortization		456,553		409,144		369,607
Significant Non-Cash Item: Impairment of Assets		519,129
Income Tax Expense (Benefit)		9,783		165,680		121,055
Significant Item: Gain on Sale of Assets						12,736
Segment Profit: Net Income (Loss)		79,718		480,895		578,680
Expenditures for Additions to Long-Lived Assets		941,045		1,122,819		828,176
Segment Assets		8,476,875		8,402,098		8,080,507
Exploration and Production
Segment Reporting Information [Line Items]
Significant Non-Cash Item: Impairment of Assets		473,054
Exploration and Production | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	961,078	[2]	958,455	[3]	1,010,464
Intersegment Revenues		0		0		0
Interest Income		2,729		3,259		1,929
Interest Expense		59,799		54,317		53,401
Depreciation, Depletion and Amortization		277,945		241,142		208,148
Income Tax Expense (Benefit)		(58,430)		87,796		43,898
Significant Item: Gain on Sale of Assets						12,736
Segment Profit: Net Income (Loss)		(163,954)		232,275		306,064
Expenditures for Additions to Long-Lived Assets		536,349		737,725		565,791
Segment Assets		2,644,820		2,814,218		2,507,541
Operating Revenues		961,078		958,455		1,010,464
Exploration and Production | Total Reportable Segments | Customer Concentration Risk | Three Customers | Revenue Benchmark
Segment Reporting Information [Line Items]
Operating Revenues						850,000
Exploration and Production | Total Reportable Segments | Customer Concentration Risk | One Customer | Revenue Benchmark
Segment Reporting Information [Line Items]
Operating Revenues				208,000
Pipeline and Storage | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	271,388	[2]	259,646	[3]	265,415
Intersegment Revenues		141,005		119,545		111,629
Interest Income		8,632		7,052		2,275
Interest Expense		47,428		43,499		42,492
Depreciation, Depletion and Amortization		74,530		70,827		67,701
Significant Non-Cash Item: Impairment of Assets		46,075
Income Tax Expense (Benefit)		26,045		34,489		35,043
Significant Item: Gain on Sale of Assets						0
Segment Profit: Net Income (Loss)		79,670		100,501		102,557
Expenditures for Additions to Long-Lived Assets		110,830		141,877		95,806
Segment Assets		2,446,243		2,427,214		2,394,697
Operating Revenues		412,393		379,191		377,044
Pipeline and Storage | Total Reportable Segments | Customer Concentration Risk | Three Customers | Revenue Benchmark
Segment Reporting Information [Line Items]
Operating Revenues						15,000
Pipeline and Storage | Total Reportable Segments | Customer Concentration Risk | One Customer | Revenue Benchmark
Segment Reporting Information [Line Items]
Operating Revenues				14,000
Gathering | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	15,537	[2]	13,891	[3]	12,086
Intersegment Revenues		228,688		216,426		202,757
Interest Income		333		534		198
Interest Expense		14,206		14,989		16,488
Depreciation, Depletion and Amortization		38,817		35,725		33,998
Significant Non-Cash Item: Impairment of Assets		0
Income Tax Expense (Benefit)		38,217		36,128		24,949
Significant Item: Gain on Sale of Assets						0
Segment Profit: Net Income (Loss)		106,913		99,724		101,111
Expenditures for Additions to Long-Lived Assets		109,251		103,295		55,546
Segment Assets		987,103		912,923		878,796
Operating Revenues		244,225		230,317		214,843
Utility | Total Reportable Segments
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	696,807	[2]	941,779	[3]	897,916
Intersegment Revenues		555		581		305
Interest Income		5,736		6,296		2,730
Interest Expense		34,727		34,233		24,115
Depreciation, Depletion and Amortization		65,261		61,450		59,760
Significant Non-Cash Item: Impairment of Assets		0
Income Tax Expense (Benefit)		3,951		7,267		17,165
Significant Item: Gain on Sale of Assets						0
Segment Profit: Net Income (Loss)		57,089		48,395		68,948
Expenditures for Additions to Long-Lived Assets		184,615		139,922		111,033
Segment Assets		2,398,709		2,247,743		2,299,473
Operating Revenues		697,362		942,360		898,221
All Other | All Other
Segment Reporting Information [Line Items]
Revenues From External Customers	[1]	0	[2]	0	[3]	0
Intersegment Revenues		0		0		6
Interest Income		0		0		3
Interest Expense		374		157		4
Depreciation, Depletion and Amortization		0		0		0
Significant Non-Cash Item: Impairment of Assets		0
Income Tax Expense (Benefit)		(186)		(164)		3
Significant Item: Gain on Sale of Assets						0
Segment Profit: Net Income (Loss)		(617)		(531)		(9)
Expenditures for Additions to Long-Lived Assets		0		0		0
Segment Assets		$ 6,227		$ 4,795		$ 2,036

[1] All Revenue from External Customers originated in the United States.

[2] Revenue from one customer of the Company’s Exploration and Production segment, exclusive of hedging losses transacted with separate parties, represented approximately $208 million of the Company’s consolidated revenue for the year ended September 30, 2023. This one customer was also a customer of the Company’s Pipeline and Storage segment, accounting for an additional $14 million of the Company’s consolidated revenue for the year ended September 30, 2023.

[3] Revenues from three customers of the Company’s Exploration and Production segment, exclusive of hedging losses transacted with separate parties, represented approximately $850 million of the Company’s consolidated revenue for the year ended September 30, 2022. These three customers were also customers of the Company’s Pipeline and Storage segment, accounting for an additional $15 million of the Company’s consolidated revenue for the year ended September 30, 2022.