Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended													12 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010	Dec. 31, 2011 Exploration And Production [Member]	Sep. 30, 2011 Exploration And Production [Member]	Dec. 31, 2010 Exploration And Production [Member]	Sep. 30, 2010 Exploration And Production [Member]	Dec. 31, 2011 All Other [Member]	Sep. 30, 2011 All Other [Member]	Dec. 31, 2011 Pipeline And Storage [Member]	Sep. 30, 2011 Pipeline And Storage [Member]	Dec. 31, 2010 Pipeline And Storage [Member]	Dec. 31, 2011 Utility [Member]	Dec. 31, 2010 Stock Options [Member]	Dec. 31, 2011 Restricted Share Awards [Member]	Dec. 31, 2011 Restricted Share Units [Member]	Dec. 31, 2011 Nonperformance Based Stock Appreciation Right [Member]	Dec. 31, 2011 Performance Based Stock Appreciation Right [Member] Stock Options [Member]	Dec. 31, 2011 Exchange-Traded Futures Contracts [Member]	Sep. 30, 2011 Exchange-Traded Futures Contracts [Member]	Dec. 31, 2011 Over-The-Counter Crude Oil Swap Agreements [Member]	Sep. 30, 2011 Over-The-Counter Crude Oil Swap Agreements [Member]
Summary Of Significant Accounting Policies [Line Items]
Accrued capital expenditure, non-cash investing activity				$ 88,100,000	$ 63,500,000	$ 60,700,000	$ 55,500,000	$ 14,500,000	$ 1,400,000	$ 15,800,000	$ 7,300,000	$ 2,000,000
Hedging collateral deposits	25,118,000	19,701,000																	4,500,000	5,500,000	20,600,000	14,200,000
Antidilutive securities	191,285		23,478
Share based compensation other than options grants in period															41,525	56,000	166,000
Share based compensation arrangement by share based payment award other than options grants in period weighted average grant date excise price																	$ 55.09
Granted in 2011, weighted average grant date fair value															$ 55.09	$ 48.77	$ 11.20
Tax benefit total not realized due to tax loss carryforwards	14,200,000	18,100,000												18,100,000				14,200,000
Gas stored underground - current	50,808,000	54,325,000											7,100,000
Capitalized costs of unproved properties excluded from amortization	226,500,000	226,300,000
Full cost ceiling test discount factor	10.00%
Amount full cost ceiling exceeds book value of oil and gas properties	$ 360,300,000