Long-Term Debt (Schedule Of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 764,583	$ 764,563
6 5/8% Senior Notes Due 2016 [Member]
Debt Instrument [Line Items]
Senior notes	249,694	249,674
Stated interest rate	6.625%
Maturity	2016
6 1/2% Senior Notes Due 2029 [Member]
Debt Instrument [Line Items]
Senior notes	100,000	100,000
Stated interest rate	6.50%
Maturity	2029
6 3/4% Senior Notes Due 2032 [Member]
Debt Instrument [Line Items]
Senior notes	250,000	250,000
Stated interest rate	6.75%
Maturity	2032
2035 GO Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Senior notes	89,000	89,000
Stated interest rate	6.50%
Maturity	2035
2035 IKE Zone 6 1/2% Notes [Member]
Debt Instrument [Line Items]
Senior notes	65,000	65,000
Stated interest rate	6.50%
Maturity	2035
Loan Related To Tax-Exempt Waste Disposal Revenue Bonds Due 2027 [Member]
Debt Instrument [Line Items]
Non-current loan payable	$ 10,889	$ 10,889
Maturity	2027