Fair Value (Schedule Of Recurring Fair Value Measurements Of Commodity Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	$ 3,065	$ 2,510
Energy commodity derivatives contracts (current assets)	13,878	4,914
Forward-starting interest rate swap agreements (noncurrent)	1,008
Energy commodity derivatives contracts (noncurrent liabilities)	(2,008)	(6,457)
Debt	(2,426,955)	(2,389,700)
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Energy commodity derivatives contracts (current assets)	13,878	4,914
Energy commodity derivatives contracts (noncurrent liabilities)	(2,008)	(6,457)
Debt	(2,426,955)	(2,389,700)
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward-starting interest rate swap agreements (noncurrent)	1,008
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	$ 3,065	$ 2,510