Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Long Term Debt
Total long-term debt including current maturities	$ 2,677,003		$ 2,815,439
Less current maturities	150,602		134,762
Total long-term debt	2,526,401		2,680,677
Estimated fair value of long-term debt	2,766,835		2,796,504
7.50% notes due 2021
Long Term Debt
Total long-term debt including current maturities	600,000	[1]	600,000	[1]
Line of Credit
Long Term Debt
Total long-term debt including current maturities	0		0
5.60% notes due 2012
Long Term Debt
Total long-term debt including current maturities	0	[2]	134,508	[2]
6.30% notes due 2013
Long Term Debt
Total long-term debt including current maturities	140,413	[3]	140,352	[3]
10.125% notes due 2015
Long Term Debt
Total long-term debt including current maturities	152,718	[4]	153,464	[4]
6.50% notes due 2016
Long Term Debt
Total long-term debt including current maturities	515,060	[5]	518,293	[5]
6.40% notes due 2017
Long Term Debt
Total long-term debt including current maturities	349,888	[6]	349,869	[6]
7.00% notes due 2018
Long Term Debt
Total long-term debt including current maturities	399,731	[7]	399,693	[7]
10.375% notes due 2018
Long Term Debt
Total long-term debt including current maturities	248,676	[8]	248,526	[8]
7.15% notes due 2037
Long Term Debt
Total long-term debt including current maturities	239,553	[9]	239,545	[9]
Medium-term Notes
Long Term Debt
Total long-term debt including current maturities	16,000		16,000
Industrial Revenue Bonds
Long Term Debt
Total long-term debt including current maturities	14,000		14,000
Other Notes
Long Term Debt
Total long-term debt including current maturities	$ 964		$ 1,189

[1] The effective interest rate for these notes is 7.75%.

[2] Includes decreases for unamortized discounts, as follows: December 31, 2011 - $49 thousand.

[3] Includes decreases for unamortized discounts, as follows: December 31, 2012 - $30 thousand and December 31, 2011 - $92 thousand. The effective interest rate for these notes is 7.48%.

[4] Includes an increase for the unamortized portion of the deferred gain realized upon the August 2011 settlement of interest rate swaps, as follows: December 31, 2012 - $2,983 thousand and December 31, 2011 - $3,802 thousand. Additionally, includes decreases for unamortized discounts, as follows: December 31, 2012 - $265 thousand and December 31, 2011 - $338 thousand. The effective interest rate for these notes is 9.59%.

[5] Includes an increase for the unamortized portion of the deferred gain realized upon the August 2011 settlement of interest rate swaps, as follows: December 31, 2012 - $15,060 thousand and December 31, 2011 - $18,293 thousand. The effective interest rate for these notes is 6.02%.

[6] Includes decreases for unamortized discounts, as follows: December 31, 2012 - $112 thousand and December 31, 2011 - $131 thousand. The effective interest rate for these notes is 7.41%.

[7] Includes decreases for unamortized discounts, as follows: December 31, 2012 - $269 thousand and December 31, 2011 - $307 thousand. The effective interest rate for these notes is 7.87%.

[8] Includes decreases for unamortized discounts, as follows: December 31, 2012 - $1,324 thousand and December 31, 2011 - $1,474 thousand. The effective interest rate for these notes is 10.62%.

[9] Includes decreases for unamortized discounts, as follows: December 31, 2012 - $635 thousand and December 31, 2011 - $643 thousand. The effective interest rate for these notes is 8.05%.