Derivative Instruments Derivative Instruments (Details 2) (Full 2013 Term [Member], Natural Gas [Member])	Sep. 30, 2012
Natural Gas Sales - Three-way collars - Derivative 1 [Member]
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	1,000
Natural Gas Sales - Three-way collars - Derivative 2 [Member]
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	1,000
Natural Gas Sales - Three-way collars - Derivative 3 [Member]
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	1,000
Natural Gas Sales - Three-way collars - Derivative 4 [Member]
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	2,000
Sold Put | Natural Gas Sales - Three-way collars - Derivative 1 [Member]
Derivative instruments
Put (in dollars per MMBtu)	2.9
Sold Put | Natural Gas Sales - Three-way collars - Derivative 2 [Member]
Derivative instruments
Put (in dollars per MMBtu)	2.96
Sold Put | Natural Gas Sales - Three-way collars - Derivative 3 [Member]
Derivative instruments
Put (in dollars per MMBtu)	2.70
Sold Put | Natural Gas Sales - Three-way collars - Derivative 4 [Member]
Derivative instruments
Put (in dollars per MMBtu)	3.03
Purchased Call | Natural Gas Sales - Three-way collars - Derivative 1 [Member]
Derivative instruments
Call (in dollars per MMBtu)	4
Purchased Call | Natural Gas Sales - Three-way collars - Derivative 2 [Member]
Derivative instruments
Call (in dollars per MMBtu)	4.25
Purchased Call | Natural Gas Sales - Three-way collars - Derivative 3 [Member]
Derivative instruments
Call (in dollars per MMBtu)	4
Purchased Call | Natural Gas Sales - Three-way collars - Derivative 4 [Member]
Derivative instruments
Call (in dollars per MMBtu)	4.25
Sold Call | Natural Gas Sales - Three-way collars - Derivative 1 [Member]
Derivative instruments
Call (in dollars per MMBtu)	5
Sold Call | Natural Gas Sales - Three-way collars - Derivative 2 [Member]
Derivative instruments
Call (in dollars per MMBtu)	5.25
Sold Call | Natural Gas Sales - Three-way collars - Derivative 3 [Member]
Derivative instruments
Call (in dollars per MMBtu)	5
Sold Call | Natural Gas Sales - Three-way collars - Derivative 4 [Member]
Derivative instruments
Call (in dollars per MMBtu)	5.25