Derivative Instruments (Details 2) (2013, Natural Gas)	Jun. 30, 2012
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	8,000
Three-way collars - Derivative 1
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	1,000
Three-way collars - Derivative 2
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	1,000
Three-way collars - Derivative 3
Derivative instruments
Notional amount of derivatives (Bbl/MMBtu per day)	1,000
Sold Put | Three-way collars - Derivative 1
Derivative instruments
Put (in dollars per MMBtu)	2.90
Sold Put | Three-way collars - Derivative 2
Derivative instruments
Put (in dollars per MMBtu)	2.96
Sold Put | Three-way collars - Derivative 3
Derivative instruments
Put (in dollars per MMBtu)	2.70
Purchased Call | Three-way collars - Derivative 1
Derivative instruments
Call (in dollars per MMBtu)	4.00
Purchased Call | Three-way collars - Derivative 2
Derivative instruments
Call (in dollars per MMBtu)	4.25
Purchased Call | Three-way collars - Derivative 3
Derivative instruments
Call (in dollars per MMBtu)	4.00
Sold Call | Three-way collars - Derivative 1
Derivative instruments
Call (in dollars per MMBtu)	5.00
Sold Call | Three-way collars - Derivative 2
Derivative instruments
Call (in dollars per MMBtu)	5.25
Sold Call | Three-way collars - Derivative 3
Derivative instruments
Call (in dollars per MMBtu)	5.00