Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
INCOME
Operating Revenues	$ 342,912	$ 348,368	$ 1,303,473	$ 1,292,944
Operating Expenses:
Property, Franchise and Other Taxes	20,595	21,447	64,245	64,368
Depreciation, Depletion and Amortization	60,817	55,617	177,802	168,812
Total Operating Expenses	235,152	225,014	897,016	827,494
Operating Income	107,760	123,354	406,457	465,450
Other Income (Expense):
Interest Income	1,632	853	4,907	2,844
Other Income	999	1,370	3,492	4,728
Interest Expense on Long-Term Debt	(27,177)	(29,225)	(82,412)	(87,241)
Other Interest Expense	(1,006)	(846)	(2,742)	(2,680)
Income Before Income Taxes	82,208	95,506	329,702	383,101
Income Tax Expense (Benefit)	19,183	35,792	(23,825)	145,195
Net Income Available for Common Stock	63,025	59,714	353,527	237,906
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,070,939	817,348	851,669	676,361
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,133,964	877,062	1,205,196	914,267
Dividends on Common Stock	(36,526)	(35,469)	(107,758)	(104,590)
Cumulative Effect of Adoption of Authoritative Guidance for Stock-Based Compensation	0	0	0	31,916
Balance at June 30	$ 1,097,438	$ 841,593	$ 1,097,438	$ 841,593
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in dollars per share)	$ 0.73	$ 0.70	$ 4.12	$ 2.79
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in dollars per share)	$ 0.73	$ 0.69	$ 4.09	$ 2.77
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	85,930,289	85,422,313	85,789,279	85,315,154
Used in Diluted Calculation (shares)	86,501,194	86,064,464	86,370,900	85,950,742
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.425	$ 0.415	$ 1.255	$ 1.225
Purchased Gas [Member]
Operating Expenses:
Purchased Gas	$ 52,211	$ 46,135	$ 322,854	$ 264,349
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	154,088	146,360	719,234	663,029
Operating Expenses:
Operation and Maintenance	45,618	44,467	158,397	158,796
Exploration and Production and Other [Member]
INCOME
Operating Revenues	137,492	151,925	425,811	473,617
Operating Expenses:
Operation and Maintenance	31,141	34,098	106,268	102,153
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	51,332	50,083	158,428	156,298
Operating Expenses:
Operation and Maintenance	$ 24,770	$ 23,250	$ 67,450	$ 69,016