Fair Value Measurements (Summary Of Carrying And Fair Values Of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
6 5/8% Senior Notes Due 2016 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, Carrying Value	$ 249,694	$ 249,674
Senior Notes, Fair Value	255,000	254,890
Stated interest rate	6.625%
Maturity date	2016
6 1/2% Senior Notes Due 2029 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, Carrying Value	100,000	100,000
Senior Notes, Fair Value	112,316	108,834
Stated interest rate	6.50%
Maturity date	2029
6 3/4% Senior Notes Due 2032 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, Carrying Value	250,000	250,000
Senior Notes, Fair Value	274,348	263,988
Stated interest rate	6.75%
Maturity date	2032
2035 GO Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, Carrying Value	89,000	89,000
Senior Notes, Fair Value	96,091	93,090
Stated interest rate	6.50%
Maturity date	2035
2035 IKE Zone 6 1/2% Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes, Carrying Value	65,000	65,000
Senior Notes, Fair Value	70,179	67,987
Stated interest rate	6.50%
Maturity date	2035
Loan Related To Tax-Exempt Waste Disposal Revenue Bonds Due 2027 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, Carrying Value	10,889	10,889
Loans, Fair Value	$ 10,889	$ 10,889
Maturity date	2027