Financial Instruments (Narrative) (Details) (USD $)	9 Months Ended				3 Months Ended	9 Months Ended
	Jun. 30, 2014 counterparty		Sep. 30, 2013		Jun. 30, 2014 Over Counter Swaps Oil [Member]	Jun. 30, 2014 Over Counter Swaps Oil [Member]	Jun. 30, 2014 Over-The-Counter Swap Position	Jun. 30, 2014 Fixed Price Purchase Commitments MMCf [Member] Energy Marketing [Member] MMcf	Jun. 30, 2014 Fair Value Hedges MMCf [Member] Energy Marketing [Member] MMcf	Jun. 30, 2014 Fixed Price Sales Commitments MMCf [Member] Energy Marketing [Member] MMcf	Jun. 30, 2014 Natural Gas MMCf [Member] Cash Flow Hedges Short Position [Member] MMcf	Jun. 30, 2014 Natural Gas MMCf [Member] Cash Flow Hedges Long Position [Member] MMcf	Jun. 30, 2014 Crude Oil Bbls [Member] Cash Flow Hedges Short Position [Member] bbl	Jun. 30, 2014 Exchange Traded Futures Contracts [Member]	Sep. 30, 2013 Exchange Traded Futures Contracts [Member]	Jun. 30, 2014 Equity Mutual Fund [Member]	Sep. 30, 2013 Equity Mutual Fund [Member]	Jun. 30, 2014 Insurance Company Stock [Member]	Sep. 30, 2013 Insurance Company Stock [Member]	Jun. 30, 2014 Credit Risk Related Contingency Feature [Member] Over-The-Counter Swap Position counterparty
Derivative Instruments, Gain (Loss) [Line Items]
Cash surrender value of life insurance	$ 44,000,000		$ 57,600,000
Fair value																35,700,000	31,800,000	7,900,000	6,500,000
Gross unrealized gain																8,700,000	5,700,000	5,400,000	4,100,000
Nonmonetary notional amount of price risk cash flow hedge derivatives, natural gas											221,900	3,500
Nonmonetary notional amount of price risk cash flow hedge derivatives, crude oil													3,777,000
Net hedging gains/losses in accumulated other comprehensive income (loss)	6,200,000
After tax net hedging gains (losses) in accumulated other comprehensive income (loss)	3,600,000
Pre-Tax Net Hedging Gain (Losses) Reclassified Within Twelve Months	(15,300,000)
After Tax Net Hedging Gains (Losses) Reclassified Within Twelve Months	(8,700,000)
Pre-Tax Net Hedging Gain (Losses) Reclassified After Twelve Months	21,500,000
After Tax Net Hedging Gains (Losses) Reclassified After Twelve Months	12,300,000
Nonmonetary notional amount of price risk fair value hedge derivatives, natural gas								400	9,600	9,200
Derivative gain (loss)					(3,600,000)	(3,600,000)
Number of counterparties in which the company holds over-the-counter swap positions	15
Number of counterparties in net gain position	4
Credit risk exposure per counterparty							6,700,000
Maximum credit risk exposure per counterparty							12,200,000
Hedging collateral deposits	0	[1]	1,094,000	[1]			0							0	1,100,000
Number of counterparties with a common credit-risk related contingency																				12
Fair market value of derivative asset with a credit-risk related contingency	26,200,000
Fair market value of derivative liability with a credit-risk related contingency	$ 21,900,000

[1] Netting Adjustments represent the impact of legally-enforceable master netting arrangements that allow the Company to net gain and loss positions held with the same counterparties. The net asset or net liability for each counterparty is recorded as an asset or liability on the Company’s balance sheet.