Debt (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Short-term Borrowings
Bank line of credit			$ 0
Total short-term borrowings			0
Long Term Debt
Total long-term debt including current maturities	2,812,603	2,815,439	2,821,438
Less current maturities of long-term debt	285,153	134,762	5,215
Total long-term debt	2,527,450	2,680,677	2,816,223
Estimated fair value of long-term debt	2,796,358	2,796,504	2,649,207
Bank Line of Credit [Member]
Long Term Debt
Total long-term debt including current maturities	0	0
6.30% notes due 2013 [Member]
Long Term Debt
Total long-term debt including current maturities	140,398	140,352	140,337
10.125% notes due 2015 [Member]
Long Term Debt
Total long-term debt including current maturities	152,911	153,464	153,640
6.50% notes due 2016 [Member]
Long Term Debt
Total long-term debt including current maturities	515,887	518,293	519,072
6.40% notes due 2017 [Member]
Long Term Debt
Total long-term debt including current maturities	349,883	349,869	349,865
7.00% notes due 2018 [Member]
Long Term Debt
Total long-term debt including current maturities	399,721	399,693	399,684
10.375% notes due 2018 [Member]
Long Term Debt
Total long-term debt including current maturities	248,637	248,526	248,491
7.50% notes due 2021 [Member]
Long Term Debt
Total long-term debt including current maturities	600,000	600,000	600,000
7.15% notes due 2037 [Member]
Long Term Debt
Total long-term debt including current maturities	239,551	239,545	239,544
Medium-term Notes [Member]
Long Term Debt
Total long-term debt including current maturities	16,000	16,000	21,000
Industrial Revenue Bonds [Member]
Long Term Debt
Total long-term debt including current maturities	14,000	14,000	14,000
Other Notes [Member]
Long Term Debt
Total long-term debt including current maturities	1,067	1,189	1,309
5.60% notes due 2012 [Member]
Long Term Debt
Total long-term debt including current maturities	$ 134,548	$ 134,508	$ 134,496