Derivatives (Details)	Jun. 30, 2012 MMBTU	Sep. 30, 2011 MMBTU
Fixed price Three [Member]
Summary of derivative instruments contracts
Production volume covered per month	2,000
CEGT [Member] | Natural gas basis protection swaps [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000	50,000
Fixed price	0.29	0.27
CEGT [Member] | Natural gas basis protection swaps [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Production volume covered per month	40,000	50,000
Fixed price	0.30	0.27
CEGT [Member] | Natural gas basis protection swaps [Member] | Fixed price Three [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		0.29
CEGT [Member] | Natural gas basis protection swaps [Member] | Fixed price Four [Member]
Summary of derivative instruments contracts
Production volume covered per month		40,000
Fixed price		0.30
PEPL [Member] | Natural gas basis protection swaps [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000	50,000
Fixed price	0.29	0.26
PEPL [Member] | Natural gas basis protection swaps [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000	50,000
Fixed price	0.30	0.27
PEPL [Member] | Natural gas basis protection swaps [Member] | Fixed price Three [Member]
Summary of derivative instruments contracts
Production volume covered per month		70,000
Fixed price		0.36
PEPL [Member] | Natural gas basis protection swaps [Member] | Fixed price Four [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		0.29
PEPL [Member] | Natural gas basis protection swaps [Member] | Fixed price Five [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		0.30
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.63
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.65
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.65
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member] | Fixed price Three [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.70
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member] | Fixed price Four [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.75
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member] | Fixed price Five [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.50
NYMEX Henry Hub [Member] | Natural gas fixed price swaps [Member] | Fixed price Six [Member]
Summary of derivative instruments contracts
Production volume covered per month		50,000
Fixed price		4.60
NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000
NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Production volume covered per month	120,000
NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Three [Member]
Summary of derivative instruments contracts
Production volume covered per month	60,000
NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Four [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000
NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Five [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000
NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Six [Member]
Summary of derivative instruments contracts
Production volume covered per month	50,000
NYMEX WTI [Member] | Oil costless collars [Member]
Summary of derivative instruments contracts
Production volume covered per month		5,000
NYMEX WTI [Member] | Oil costless collars [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Production volume covered per month	2,000
NYMEX WTI [Member] | Oil costless collars [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Production volume covered per month	3,000
Floor [Member]
Summary of derivative instruments contracts
Fixed price	90
Floor [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Fixed price	2.50
Floor [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Fixed price	2.50
Floor [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Three [Member]
Summary of derivative instruments contracts
Fixed price	2.50
Floor [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Four [Member]
Summary of derivative instruments contracts
Fixed price	2.50
Floor [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Five [Member]
Summary of derivative instruments contracts
Fixed price	2.50
Floor [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Six [Member]
Summary of derivative instruments contracts
Fixed price	2.50
Floor [Member] | NYMEX WTI [Member] | Oil costless collars [Member]
Summary of derivative instruments contracts
Fixed price		100
Floor [Member] | NYMEX WTI [Member] | Oil costless collars [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Fixed price	90
Floor [Member] | NYMEX WTI [Member] | Oil costless collars [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Fixed price	90
Ceiling [Member]
Summary of derivative instruments contracts
Fixed price	114
Ceiling [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Fixed price	3.25
Ceiling [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Fixed price	3.10
Ceiling [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Three [Member]
Summary of derivative instruments contracts
Fixed price	3.20
Ceiling [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Four [Member]
Summary of derivative instruments contracts
Fixed price	3.20
Ceiling [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Five [Member]
Summary of derivative instruments contracts
Fixed price	3.45
Ceiling [Member] | NYMEX Henry Hub [Member] | Natural gas costless collars [Member] | Fixed price Six [Member]
Summary of derivative instruments contracts
Fixed price	3.30
Ceiling [Member] | NYMEX WTI [Member] | Oil costless collars [Member]
Summary of derivative instruments contracts
Fixed price		112
Ceiling [Member] | NYMEX WTI [Member] | Oil costless collars [Member] | Fixed price One [Member]
Summary of derivative instruments contracts
Fixed price	105
Ceiling [Member] | NYMEX WTI [Member] | Oil costless collars [Member] | Fixed price Two [Member]
Summary of derivative instruments contracts
Fixed price	110