Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
INCOME
Operating Revenues	$ 444,188	$ 490,247
Operating Expenses:
Property, Franchise and Other Taxes	23,144	24,005
Depreciation, Depletion and Amortization	74,918	64,255
Total Operating Expenses	296,168	328,564
Operating Income	148,020	161,683
Other Income (Expense):
Other Income (Deductions)	(3,040)	(9,602)
Interest Expense on Long-Term Debt	(25,443)	(25,439)
Other Interest Expense	(1,551)	(1,073)
Income Before Income Taxes	117,986	125,569
Income Tax Expense	31,395	22,909
Net Income Available for Common Stock	86,591	102,660
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,272,601	1,098,900
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,359,192	1,201,560
Dividends on Common Stock	(37,650)	(36,663)
Balance at December 31	$ 1,320,592	$ 1,172,334
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in dollars per share)	$ 1.00	$ 1.19
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in dollars per share)	$ 1.00	$ 1.18
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	86,378,450	86,032,729
Used in Diluted Calculation (shares)	86,883,152	86,708,814
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.435	$ 0.425
Purchased Gas [Member]
Operating Expenses:
Purchased Gas	$ 92,272	$ 138,660
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	228,026	272,092
Operating Expenses:
Operation and Maintenance	43,256	43,915
Exploration and Production and Other [Member]
INCOME
Operating Revenues	167,193	163,937
Operating Expenses:
Operation and Maintenance	36,693	32,795
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	48,969	54,218
Operating Expenses:
Operation and Maintenance	25,885	24,934
Guidance for Hedging [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	(950)	0
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	$ 0	$ 7,437