Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified			0 Months Ended	1 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Jul. 30, 2012 6 5/8% Senior Notes Due 2016	Jul. 31, 2012 6 5/8% Senior Notes Due 2016	Sep. 30, 2012 6 5/8% Senior Notes Due 2016	Dec. 31, 2011 6 5/8% Senior Notes Due 2016	Jul. 17, 2012 3.60% Senior Notes Due 2022	Sep. 30, 2012 3.60% Senior Notes Due 2022	Dec. 31, 2011 3.60% Senior Notes Due 2022	Sep. 30, 2012 6 1/2% Senior Notes Due 2029	Dec. 31, 2011 6 1/2% Senior Notes Due 2029	Sep. 30, 2012 6 3/4% Senior Notes Due 2032	Dec. 31, 2011 6 3/4% Senior Notes Due 2032	Sep. 30, 2012 2035 GO Zone 6 1/2% Notes	Dec. 31, 2011 2035 GO Zone 6 1/2% Notes	Sep. 30, 2012 2035 IKE Zone 6 1/2% Notes	Dec. 31, 2011 2035 IKE Zone 6 1/2% Notes	Sep. 30, 2012 Loan Related To Tax-Exempt Waste Disposal Revenue Bonds Due 2027	Dec. 31, 2011 Loan Related To Tax-Exempt Waste Disposal Revenue Bonds Due 2027
Debt Instrument [Line Items]
Maturity			2016	2016	2016		2022	2022		2029		2032		2035		2035		2027
Stated interest rate			6.625%		6.625%		3.60%	3.60%		6.50%		6.75%		6.50%		6.50%
Senior notes					$ 0	$ 249,674		$ 248,842	$ 0	$ 100,000	$ 100,000	$ 250,000	$ 250,000	$ 89,000	$ 89,000	$ 65,000	$ 65,000
Non-current loan payable																		10,889	10,889
Long-term debt	$ 763,731	$ 764,563