Supplementary Information For Oil And Gas Producing Activities (Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Future Cash Inflows	$ 10,001,545	$ 8,943,942	$ 7,373,129
Future Production Costs	2,795,657	2,334,393	1,919,530
Future Development Costs	790,033	749,876	619,573
Future Income Tax Expense at Applicable Statutory Rate	2,434,370	2,113,101	1,812,055
Future Net Cash Flows	3,981,485	3,746,572	3,021,971
10% Annual Discount for Estimated Timing of Cash Flows	1,914,607	1,780,206	1,552,180
Standardized Measure of Discounted Future Net Cash Flows	$ 2,066,878	$ 1,966,366	$ 1,469,791	$ 1,524,157

Supplementary Information For Oil And Gas Producing Activities (Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details) (USD $)
In Thousands, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]

Future Cash Inflows

$ 10,001,545

$ 8,943,942

$ 7,373,129

Future Production Costs

2,795,657

2,334,393

1,919,530

Future Development Costs

790,033

749,876

619,573

Future Income Tax Expense at Applicable Statutory Rate

2,434,370

2,113,101

1,812,055

Future Net Cash Flows

3,981,485

3,746,572

3,021,971

10% Annual Discount for Estimated Timing of Cash Flows

1,914,607

1,780,206

1,552,180

Standardized Measure of Discounted Future Net Cash Flows

$ 2,066,878

$ 1,966,366

$ 1,469,791

$ 1,524,157

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Amount of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for costs to be incurred in developing proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for income tax, based on the future income less future expense derived from production and sale of proved oil and gas reserves.

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Amount, after future accumulated cash outflow for development and production costs and future income tax, of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for costs to be incurred in producing proved oil and gas reserves.

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Amount of discount on future accumulated cash inflow, after deducting future accumulated cash outflow for development and production costs and future income tax, from sale of proved oil and gas reserves, using a discount rate of ten percent a year.

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Amount of discounted future accumulated cash inflow relating to proved oil and gas reserves.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 30

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

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-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Section 50

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-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447

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