Discontinued Operations - Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location (Details) - Natural Gas Marketing - Discontinued Operations, Disposed of by Sale $ in Thousands	9 Months Ended
	Jun. 30, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Commodity contracts	$ (9,567)
Fair value adjustment for natural gas inventory designated as the hedged item	12,858
Total decrease in purchased gas cost reflected in income from discontinued operations	3,291
The decrease in purchased gas cost reflected in income from discontinued operations is comprised of the following:
Basis ineffectiveness	(597)
Timing ineffectiveness	3,888
Total decrease in purchased gas cost reflected in income from discontinued operations	$ 3,291