Consolidated Statements Of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
OPERATING ACTIVITIES
Net Income (Loss) Available for Common Stock	$ 88,908	$ (189,109)
Adjustments to Reconcile Net Income (Loss) to Net Cash Provided by Operating Activities:
Impairment of Oil and Gas Producing Properties	0	435,451
Depreciation, Depletion and Amortization	56,196	70,551
Deferred Income Taxes	44,852	(140,013)
Excess Tax Benefits Associated with Stock-Based Compensation Awards	0	(226)
Stock-Based Compensation	2,482	960
Other	3,607	3,418
Change in:
Hedging Collateral Deposits	1,484	1,573
Receivables and Unbilled Revenue	(67,395)	(31,150)
Gas Stored Underground and Materials and Supplies	10,597	3,466
Unrecovered Purchased Gas Costs	(1,257)	0
Other Current Assets	9,576	(5,254)
Accounts Payable	18,805	(20,784)
Amounts Payable to Customers	(16,306)	(11,702)
Customer Advances	(983)	7,189
Customer Security Deposits	673	267
Other Accruals and Current Liabilities	5,919	(14,353)
Other Assets	(8,389)	885
Other Liabilities	(4,122)	2,904
Net Cash Provided by Operating Activities	144,647	114,073
INVESTING ACTIVITIES
Capital Expenditures	(106,053)	(186,437)
Net Proceeds from Sale of Oil and Gas Producing Properties	5,759	10,574
Other	(4,297)	(15,756)
Net Cash Used in Investing Activities	(104,591)	(191,619)
Financing Activities
Changes in Notes Payable to Banks and Commercial Paper	0	31,400
Excess Tax Benefits Associated with Stock-Based Compensation Awards	0	226
Dividends Paid on Common Stock	(34,473)	(33,415)
Net Proceeds from Issuance of Common Stock	938	2,068
Net Cash (Used in) Provided by Financing Activities	(33,535)	279
Net Increase (Decrease) in Cash and Temporary Cash Investments	6,521	(77,267)
Cash and Temporary Cash Investments at October 1	129,972	113,596	$ 113,596
Cash and Temporary Cash Investments at December 31	136,493	36,329	$ 129,972
Supplemental Disclosure of Cash Flow Information, Non-Cash Investing Activities:
Non-Cash Capital Expenditures	48,965	93,983
Receivable from Sale of Oil and Gas Producing Properties	$ 20,795	$ 94,364