Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
INCOME
Operating Revenues	$ 522,075	$ 449,132	$ 944,576	$ 824,327
Operating Expenses:
Purchased Gas	147,971	81,623	218,214	123,691
Property, Franchise and Other Taxes	22,542	21,305	42,921	41,662
Depreciation, Depletion and Amortization	56,999	63,947	113,194	134,498
Impairment of Oil and Gas Producing Properties	0	397,443	0	832,894
Total Operating Expenses	352,118	686,132	602,479	1,367,251
Operating Income (Loss)	169,957	(237,000)	342,097	(542,924)
Other Income (Expense):
Interest Income	391	278	1,991	2,077
Other Income	1,744	3,236	3,356	5,654
Interest Expense on Long-Term Debt	(28,913)	(28,994)	(58,016)	(59,366)
Other Interest Expense	(924)	(1,237)	(1,834)	(2,617)
Income (Loss) Before Income Taxes	142,255	(263,717)	287,594	(597,176)
Income Tax Expense (Benefit)	52,971	(116,030)	109,403	(260,380)
Net Income (Loss) Available for Common Stock	89,284	(147,687)	178,191	(336,796)
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	762,641	880,619	676,361	1,103,200
Beginning Retained Earnings Unappropriated And Current Period Net Income Loss	851,925	732,932	854,552	766,404
Dividends on Common Stock	(34,577)	(33,533)	(69,120)	(67,005)
Cumulative Effect of Adoption of Authoritative Guidance for Stock-Based Compensation	0	0	31,916	0
Balance at March 31	$ 817,348	$ 699,399	$ 817,348	$ 699,399
Earnings Per Common Share, Basic:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ 1.05	$ (1.74)	$ 2.09	$ (3.97)
Earnings Per Common Share, Diluted:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ 1.04	$ (1.74)	$ 2.07	$ (3.97)
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	85,334,887	84,806,982	85,261,575	84,728,680
Used in Diluted Calculation (shares)	86,006,614	84,806,982	85,897,282	84,728,680
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.405	$ 0.395	$ 0.810	$ 0.790
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 308,889	$ 248,173	$ 516,669	$ 417,005
Operating Expenses:
Operation and Maintenance	63,907	57,309	114,329	104,858
Exploration and Production and Other [Member]
INCOME
Operating Revenues	159,997	144,570	321,691	297,454
Operating Expenses:
Operation and Maintenance	37,593	42,964	68,055	88,539
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	53,189	56,389	106,216	109,868
Operating Expenses:
Operation and Maintenance	$ 23,106	$ 21,541	$ 45,766	$ 41,109