Derivative Instruments (Schedule Of U.S. Natural Gas Derivative Positions) (Details) (Natural Gas Derivative Positions [Member])	Jun. 30, 2013 MMBTU
2013 [Member]
Derivative [Line Items]
Volume (in MMBtu)	10,120,000
Weighted Average Floor Price ($/MMBtu)	4.58
Weighted Average Ceiling Price ($/MMBtu)	4.58
2014 [Member]
Derivative [Line Items]
Volume (in MMBtu)	18,250,000
Weighted Average Floor Price ($/MMBtu)	4.07
Weighted Average Ceiling Price ($/MMBtu)	4.36
2015 [Member]
Derivative [Line Items]
Volume (in MMBtu)	3,650,000
Weighted Average Floor Price ($/MMBtu)	4.33
Weighted Average Ceiling Price ($/MMBtu)	4.33