Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Short-term Borrowings
Bank line of credit	$ 0	$ 285,500
Total short-term borrowings	0	285,500
Long-term Debt
Total long-term debt including current maturities	2,815,439	2,432,762
Less current maturities of long-term debt	134,762	5,246
Long-term debt	2,680,677	2,427,516
Estimated fair value of total long-term debt	2,796,504	2,559,059
6.30% notes due 2013 [Member]
Long-term Debt
Total long-term debt including current maturities	140,352	249,729
Bank line of credit [Member]
Long-term Debt
Total long-term debt including current maturities	0	0
5.60% notes due 2012 [Member]
Long-term Debt
Total long-term debt including current maturities	134,508	299,773
Floating-rate term loan due 2015 [Member]
Long-term Debt
Total long-term debt including current maturities	0	450,000
10.125% notes due 2015 [Member]
Long-term Debt
Total long-term debt including current maturities	153,464	149,597
6.50% notes due 2016 [Member]
Long-term Debt
Total long-term debt including current maturities	518,293	0
6.40% notes due 2017 [Member]
Long-term Debt
Total long-term debt including current maturities	349,869	349,852
7.00% notes due 2018 [Member]
Long-term Debt
Total long-term debt including current maturities	399,693	399,658
10.375% notes due 2018 [Member]
Long-term Debt
Total long-term debt including current maturities	248,526	248,391
7.50% notes due 2021 [Member]
Long-term Debt
Total long-term debt including current maturities	600,000	0
7.15% notes due 2037 [Member]
Long-term Debt
Total long-term debt including current maturities	239,545	249,324
Medium-term notes [Member]
Long-term Debt
Total long-term debt including current maturities	16,000	21,000
Industrial revenue bonds [Member]
Long-term Debt
Total long-term debt including current maturities	14,000	14,000
Other notes [Member]
Long-term Debt
Total long-term debt including current maturities	$ 1,189	$ 1,438