Financial Instruments (Narrative) (Details) (USD $)					3 Months Ended
	Dec. 31, 2013 entity		Sep. 30, 2013		Dec. 31, 2013 Exploration And Production [Member]	Dec. 31, 2013 Exploration And Production [Member] Economic Hedges [Member]	Dec. 31, 2013 Energy Marketing [Member]	Dec. 31, 2013 Equity Mutual Fund [Member]	Sep. 30, 2013 Equity Mutual Fund [Member]	Dec. 31, 2013 Insurance Company Stock [Member]	Sep. 30, 2013 Insurance Company Stock [Member]	Dec. 31, 2013 Over-The-Counter Swap Position	Dec. 31, 2013 Over-The-Counter Swap Position Credit Risk Related Contingency Feature [Member] entity	Dec. 31, 2013 Fixed Price Purchase Commitments MMCf [Member] Energy Marketing [Member] MMcf	Dec. 31, 2013 Exchange-Traded Futures Contracts [Member]	Sep. 30, 2013 Exchange-Traded Futures Contracts [Member]	Dec. 31, 2013 Fair Value Hedges MMCf [Member] Energy Marketing [Member] MMcf	Dec. 31, 2013 Fixed Price Sales Commitments MMCf [Member] Energy Marketing [Member] MMcf	Dec. 31, 2013 Natural Gas MMCf [Member] Exploration And Production [Member] Cash Flow Hedges Short Position [Member] MMcf	Dec. 31, 2013 Natural Gas MMCf [Member] Energy Marketing [Member] MMcf	Dec. 31, 2013 Natural Gas MMCf [Member] Energy Marketing [Member] Cash Flow Hedges Short Position [Member] MMcf	Dec. 31, 2013 Natural Gas MMCf [Member] Energy Marketing [Member] Cash Flow Hedges Long Position [Member] MMcf	Dec. 31, 2013 Crude Oil Bbls [Member] Exploration And Production [Member] Cash Flow Hedges Short Position [Member] bbl	Dec. 31, 2013 Crude Oil Bbls [Member] Exploration And Production [Member] Economic Hedges [Member] bbl
Derivative Instruments, Gain (Loss) [Line Items]
Cash surrender value of life insurance	$ 57,600,000		$ 57,600,000
Fair value								33,700,000	31,800,000	7,800,000	6,500,000
Gross unrealized gain								7,000,000	5,700,000	5,400,000	4,100,000
Nonmonetary notional amount of price risk cash flow hedge derivatives, natural gas																			261,500	5,100	4,000	1,100
Nonmonetary notional amount of price risk cash flow hedge derivatives, crude oil																							3,771,000
Net hedging gains/losses in accumulated other comprehensive income (loss)					46,400,000		(700,000)
After tax net hedging gains (losses) in accumulated other comprehensive income (loss)					26,700,000		(400,000)
Pre-Tax Net Hedging Gain (Losses) Reclassified Within Twelve Months					(100,000)
After Tax Net Hedging Gains (Losses) Reclassified Within Twelve Months					(100,000)
Pre-Tax Net Hedging Gain (Losses) Reclassified After Twelve Months					46,500,000
After Tax Net Hedging Gains (Losses) Reclassified After Twelve Months					26,800,000
Nonmonetary notional amount of price risk derivatives instruments																								696,000
Derivative gain (loss)						400,000
Number of counterparties in which the company holds over-the-counter swap positions	15
Number of counterparties with a common credit-risk related contingency													12
Number of counterparties in net gain position	8
Credit risk exposure per counterparty												6,500,000
Maximum credit risk exposure per counterparty												17,500,000
Fair market value of derivative asset with a credit-risk related contingency	47,500,000
Fair market value of derivative liability with a credit-risk related contingency	5,900,000
Hedging collateral deposits	$ 0	[1]	$ 1,094,000	[1]								$ 0			$ 0	$ 1,100,000
Nonmonetary notional amount of price risk fair value hedge derivatives, natural gas														600			9,700	9,100

[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.