Consolidated Statements Of Income And Earnings Reinvested In The Business - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
INCOME
Operating Revenues	$ 1,452,416	$ 1,760,913	$ 2,113,081
Operating Expenses:
Purchased Gas	147,982	349,984	605,838
Property, Franchise and Other Taxes	81,714	89,564	90,711
Depreciation, Depletion and Amortization	249,417	336,158	383,781
Impairment of Oil and Gas Producing Properties	948,307	1,126,257	0
Total Operating Expenses	1,868,934	2,371,966	1,543,408
Operating Income (Loss)	(416,518)	(611,053)	569,673
Other Income (Expense):
Other Income	9,820	8,039	9,461
Interest Income	4,235	3,922	4,170
Interest Expense on Long-Term Debt	(117,347)	(95,916)	(90,194)
Other Interest Expense	(3,697)	(3,555)	(4,083)
Income (Loss) Before Income Taxes	(523,507)	(698,563)	489,027
Income Tax Expense (Benefit)	(232,549)	(319,136)	189,614
Net Income (Loss) Available for Common Stock	(290,958)	(379,427)	299,413
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	1,103,200	1,614,361	1,442,617
Beginning Retained Earnings Unappropriated And Current Period Net Income Loss	812,242	1,234,934	1,742,030
Dividends on Common Stock	(135,881)	(131,734)	(127,669)
Balance at End of Year	$ 676,361	$ 1,103,200	$ 1,614,361
Earnings Per Common Share, Basic:
Net Income (Loss) Available for Common Stock (in usd per share)	$ (3.43)	$ (4.50)	$ 3.57
Earnings Per Common Share, Diluted:
Net Income (Loss) Available for Common Stock (in usd per share)	$ (3.43)	$ (4.50)	$ 3.52
Weighted Average Number of Shares Outstanding:
Used in Basic Calculation	84,847,993	84,387,755	83,929,989
Used in Diluted Calculation	84,847,993	84,387,755	84,952,347
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 624,602	$ 860,618	$ 1,103,149
Operating Expenses:
Operation and Maintenance	192,512	203,249	196,534
Exploration and Production and Other Category [Member]
INCOME
Operating Revenues	611,766	696,709	808,595
Operating Expenses:
Operation and Maintenance	160,201	184,024	188,622
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	216,048	203,586	201,337
Operating Expenses:
Operation and Maintenance	$ 88,801	$ 82,730	$ 77,922