Discontinued Operations (Details) (USD $)	3 Months Ended									12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax										$ 8,203,000	$ 9,868,000		$ 0
Discontinued Operation Income Loss From Discontinued Operation Disclosures Abstract
Operating revenues										37,962,000	114,703,000		141,227,000
Purchased gas cost										21,464,000	62,902,000		83,537,000
Gross profit										16,498,000	51,801,000		57,690,000
Operating expenses										5,858,000	24,174,000		27,362,000
Operating income										10,640,000	27,627,000		30,328,000
Discontinued Operations Miscellaneous Income Expense										548,000	611,000		57,000
Income from discontinued operations before income taxes										11,188,000	28,238,000		30,385,000
Income tax expense										3,986,000	10,066,000		12,372,000
Income (loss) from discontinued operations	0	0	4,085,000	3,117,000	1,904,000		3,118,000	7,027,000	6,123,000	7,202,000	18,172,000		18,013,000
Gain on sale of discontinued operations, net of tax	0	5,294,000	0	0	6,349,000		0	0	0	5,294,000	6,349,000		0
Net income (loss) from discontinued operations										12,496,000	24,521,000		18,013,000
Disposal Group Including Discontinued Operation Balance Sheet Disclosures Abstract
Net plant, property & equipment					142,865,000						142,865,000
Gas stored underground					4,688,000						4,688,000
Other current assets					6,931,000						6,931,000
Deferred charges and other assets					87,000						87,000
Assets held for sale	0				154,571,000	[1]				0	154,571,000	[1]
Accounts payable					2,114,000						2,114,000
Other current liabilities					3,776,000						3,776,000
Regulatory cost of removal					3,257,000						3,257,000
Deferred credits and other liabilities					2,426,000						2,426,000
Liabilities held for sale	0				11,573,000					0	11,573,000
Missouri, Illinois and Iowa [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Cash Price Received from Disposal of Discontinued Operation											128,000,000
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax											9,900,000
Georgia [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Cash Price Received from Disposal of Discontinued Operation										153,000,000
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax										$ 8,200,000

[1] As discussed in Note 16, assets and liabilities related to our Georgia operations were classified as “assets held for sale” in other current assets and liabilities in our consolidated balance sheets at September 30, 2012.