Business Segment Information (Segment Information By Segment) (Details) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue		$ 287,989		$ 323,019		$ 491,095		$ 444,188	$ 293,341	$ 357,200	$ 552,544	$ 490,247		$ 1,546,291	$ 1,693,332	$ 1,592,668
Interest Income														5,007	6,065	6,766
Interest Expense														117,077	106,756	114,522
Depreciation, Depletion and Amortization														306,158	275,660	240,961
Income Tax Expense (Benefit)														18,739	85,221	(7,494)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties		253,400		18,200		177,800								449,438	0	0
Segment Profit: Net Income (Loss)		(145,545)	[1]	$ 41,250	[2]	$ (106,068)	[3]	$ 86,591	47,282	$ 63,753	$ 90,595	$ 102,660	[4]	(123,772)	304,290	391,521
Expenditures for Additions to Long-Lived Assets														1,228,617	781,246	600,602
Segment Assets		6,964,935							6,462,157					6,964,935	6,462,157	6,036,486
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue														607,453	632,740
Interest Income														698	1,107	1,479
Interest Expense														58,098	54,777	54,288
Depreciation, Depletion and Amortization														172,124	154,784	124,274
Income Tax Expense (Benefit)														(41,472)	32,978	(41,962)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														449,438
Segment Profit: Net Income (Loss)														(326,904)	111,807	180,632
Expenditures for Additions to Long-Lived Assets														670,455	491,889	380,677
Segment Assets		1,979,028							1,972,776					1,979,028	1,972,776	1,568,563
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue														309,604	288,283
Interest Income														1,475	2,982	2,748
Interest Expense														32,731	29,142	31,383
Depreciation, Depletion and Amortization														53,951	44,947	43,463
Income Tax Expense (Benefit)														28,613	23,238	17,806
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														0
Segment Profit: Net Income (Loss)														78,860	74,011	97,246
Expenditures for Additions to Long-Lived Assets														166,652	143,005	92,832
Segment Assets		2,204,971							1,893,514					2,204,971	1,893,514	1,848,180
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue														142,893	127,075
Interest Income														545	546	1,106
Interest Expense														10,877	9,406	9,560
Depreciation, Depletion and Amortization														22,440	20,038	17,313
Income Tax Expense (Benefit)														18,191	20,895	(17,677)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														0
Segment Profit: Net Income (Loss)														68,631	58,413	83,519
Expenditures for Additions to Long-Lived Assets														297,806	49,650	61,728
Segment Assets		945,199							547,995					945,199	547,995	533,608
Utility [Member]
Segment Reporting Information [Line Items]
Revenue														652,298	727,442
Interest Income														2,262	1,809	1,591
Interest Expense														22,150	23,443	26,753
Depreciation, Depletion and Amortization														55,248	53,832	53,253
Income Tax Expense (Benefit)														13,274	13,967	15,258
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														0
Segment Profit: Net Income (Loss)														57,366	60,871	51,217
Expenditures for Additions to Long-Lived Assets														94,273	95,847	85,648
Segment Assets		2,067,852							1,991,338					2,067,852	1,991,338	1,921,971
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue														1,712,248	1,775,540
Interest Income														4,980	6,444	6,924
Interest Expense														123,856	116,768	121,984
Depreciation, Depletion and Amortization														303,763	273,601	238,303
Income Tax Expense (Benefit)														18,606	91,078	(26,575)
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														449,438
Segment Profit: Net Income (Loss)														(122,047)	305,102	412,614
Expenditures for Additions to Long-Lived Assets														1,229,186	780,391	620,885
Segment Assets		7,197,050							6,405,623					7,197,050	6,405,623	5,872,322
All Other [Member]
Segment Reporting Information [Line Items]
Revenue														90,271	149,709
Interest Income														860	1,291	1,073
Interest Expense														66	21	22
Depreciation, Depletion and Amortization														1,716	1,291	1,902
Income Tax Expense (Benefit)														210	(955)	2,125
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														0
Segment Profit: Net Income (Loss)														(269)	(1,811)	261
Expenditures for Additions to Long-Lived Assets														39	128	41
Segment Assets		113,571							122,241					113,571	122,241	129,080
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue														(256,228)	(231,917)
Interest Income														(833)	(1,670)	(1,231)
Interest Expense														(6,845)	(10,033)	(7,484)
Depreciation, Depletion and Amortization														679	768	756
Income Tax Expense (Benefit)														(77)	(4,902)	16,956
Significant Non-Cash Item: Impairment of Oil and Gas Producing Properties														0
Segment Profit: Net Income (Loss)														(1,456)	999	(21,354)
Expenditures for Additions to Long-Lived Assets														(608)	727	(20,324)
Segment Assets		$ (345,686)							$ (65,707)					(345,686)	(65,707)	35,084
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													1,546,291	1,693,332	1,592,668
Revenue from External Customers [Member] | Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													607,453	632,740	564,547
Revenue from External Customers [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													205,998	195,808	210,345
Revenue from External Customers [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													72	11	41
Revenue from External Customers [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													642,855	715,813	674,726
Revenue from External Customers [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													1,456,378	1,544,372	1,449,659
Revenue from External Customers [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													89,435	148,582	142,349
Revenue from External Customers [Member] | Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	[5]													478	378	660
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue														0	0	0
Intersegment Revenues [Member] | Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue														0	0	0
Intersegment Revenues [Member] | Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue														103,606	92,475	89,981
Intersegment Revenues [Member] | Gathering [Member]
Segment Reporting Information [Line Items]
Revenue														142,821	127,064	107,856
Intersegment Revenues [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenue														9,443	11,629	12,800
Intersegment Revenues [Member] | Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue														255,870	231,168	210,637
Intersegment Revenues [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Revenue														836	1,127	826
Intersegment Revenues [Member] | Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue														$ (256,706)	$ (232,295)	$ (211,463)

[1] Includes a non-cash $253.4 million impairment charge ($183.7 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[2] Includes a non-cash $18.2 million impairment charge ($13.3 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $177.8 million impairment charge ($129.3 million after tax) associated with the Exploration and Production segment's oil and gas producing properties and a $56.8 million valuation allowance recorded against certain deferred tax assets.

[4] Includes a $5.0 million reduction to income tax expense associated with the remeasurement of accumulated deferred income taxes in accordance with the 2017 Tax Reform Act.

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