Long-Term Debt (Long-Term Debt) (Details) (USD $)	6 Months Ended
	Jun. 30, 2011	Apr. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Total debt	$ 1,085,915,000		$ 1,030,759,000	$ 1,056,085,000
Less current maturities	(106,959,000)		(248,714,000)	(244,147,000)
Long-term debt	978,956,000		782,045,000	811,938,000
Revolving Facility Interest Rate Of 1.56% [Member]
Credit Facility interest rate	1.56%
AR Credit Facility [Member]
Credit Facility	100,000,000		0	25,000,000
6.6% Senior Notes, Due 2018 [Member]
Total debt	298,380,000		298,288,000	298,198,000
Interest rate on notes	6.60%
Maturity date	2018
7% Debentures, Due 2025 [Member]
Total debt	124,405,000		124,393,000	124,382,000
Interest rate on notes	7.00%
Maturity date	2025
6.25% Senior Notes, Due 2037 [Member]
Total debt	247,898,000		247,882,000	247,866,000
Interest rate on notes	6.25%
Maturity date	2037
6.875% Notes, Due 2011 [Member]
Total debt			242,129,000	242,109,000
Interest rate on notes	6.875%	6.875%
Maturity date	2011
Term Loan Facility, Due 2015, Interest Rate Of 1.87% At June 30, 2011 [Member]
Total debt	250,000,000
Interest rate on term loan	1.87%
Maturity date	2015
Term Loan, Due 2012, Interest Rate Of 3.29% At December 31, 2010 [Member]
Total debt			111,750,000	111,750,000
Interest rate on term loan	3.29%
Maturity date	2012
Revolving Facility, Interest Rate Of 1.56% At June 30, 2011 [Member]
Credit Facility	60,000,000
AR Credit Facility, interest rate of 1.60% at June 30, 2011 [Member]
Credit Facility	100,000,000			25,000,000
Credit Facility interest rate	1.60%
Other Notes [Member]
Other notes	$ 5,232,000		$ 6,317,000	$ 6,780,000