Summary of Carrying and Fair Values of Long Term Debt (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2012
6 5/8% Senior Notes Due 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	6.625%
Maturity date	2016
6 1/2% Senior Notes Due 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	6.50%
Maturity date	2029
6 3/4% Senior Notes Due 2032
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	6.75%
Maturity date	2032
2035 GO Zone 6 1/2% Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	6.50%
Maturity date	2035
2035 IKE Zone 6 1/2% Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated interest rate	6.50%
Maturity date	2035
Loan Related To Tax-Exempt Waste Disposal Revenue Bonds Due 2027
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity date	2027