Fair Value Measurements (Schedule Of Fair Value Of Financial Assets And Liablilities By Level) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset derivative instruments	$ 123,932	$ 103,253
Liability derivative instruments	19,332	26,475
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from commodity derivative instruments	123,932	103,233
Assets from interest rate derivative instruments		20
Liabilities from commodity derivative instruments	6,062	2,502
Liabilities from interest rate derivative instruments	13,270	23,973
Asset derivative instruments	123,932	103,253
Liability derivative instruments	19,332	26,475
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets from commodity derivative instruments	123,932	103,233
Assets from interest rate derivative instruments		20
Liabilities from commodity derivative instruments	6,062	2,502
Liabilities from interest rate derivative instruments	13,270	23,973
Asset derivative instruments	123,932	103,253
Liability derivative instruments	$ 19,332	$ 26,475