Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
INCOME
Operating Revenues	$ 422,500	$ 375,195
Operating Expenses:
Purchased Gas	70,243	42,068
Property, Franchise and Other Taxes	20,379	20,357
Depreciation, Depletion and Amortization	56,196	70,551
Impairment of Oil and Gas Producing Properties	0	435,451
Total Operating Expenses	250,361	681,119
Operating Income (Loss)	172,139	(305,924)
Other Income (Expense):
Interest Income	1,600	1,799
Other Income	1,614	2,418
Interest Expense on Long-Term Debt	(29,103)	(30,372)
Other Interest Expense	(910)	(1,380)
Income (Loss) Before Income Taxes	145,340	(333,459)
Income Tax Expense (Benefit)	56,432	(144,350)
Net Income (Loss) Available for Common Stock	88,908	(189,109)
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	676,361	1,103,200
Beginning Retained Earnings Unappropriated And Current Period Net Income Loss	765,269	914,091
Dividends on Common Stock	(34,544)	(33,472)
Cumulative Effect of Adoption of Authoritative Guidance for Stock-Based Compensation	31,916	0
Balance at December 31	$ 762,641	$ 880,619
Earnings Per Common Share, Basic:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ 1.04	$ (2.23)
Earnings Per Common Share, Diluted:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ 1.04	$ (2.23)
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	85,189,851	84,651,233
Used in Diluted Calculation (shares)	85,797,989	84,651,233
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.405	$ 0.395
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 207,780	$ 168,832
Operating Expenses:
Operation and Maintenance	50,422	47,549
Exploration and Production and Other [Member]
INCOME
Operating Revenues	161,694	152,884
Operating Expenses:
Operation and Maintenance	30,461	45,575
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	53,026	53,479
Operating Expenses:
Operation and Maintenance	$ 22,660	$ 19,568