Fair Value (Schedule Of Recurring Fair Value Measurements Of Commodity Contracts) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	$ 2,816	$ 2,510
Energy commodity derivatives contracts (current)	(4,654)	4,914
Energy commodity derivatives contracts (noncurrent)	(11,744)	(6,457)
Debt	(2,387,630)	(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)	(4,654)	4,914
Energy commodity derivatives contracts (noncurrent)	(11,744)	(6,457)
Debt	(2,387,630)	(2,389,700)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	$ 2,816	$ 2,510