Derivative Instruments (Schedule Of U.S. Natural Gas Derivative Positions) (Details) (Natural Gas Derivative Positions [Member])	Dec. 31, 2012 MMBTU
2013 [Member]
Derivative [Line Items]
Volume (in MMBtu)	18,250,000
Weighted Average Floor Price ($/MMBtu)	4.63
Weighted Average Ceiling Price ($/MMBtu)	4.63
2014 [Member]
Derivative [Line Items]
Volume (in MMBtu)	3,650,000
Weighted Average Floor Price ($/MMBtu)	0.00
Weighted Average Ceiling Price ($/MMBtu)	5.50