Long Term Debt (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Debt Instrument
Total debt	$ 1,078,527,000	$ 1,047,859,000	$ 1,134,828,000
Less current maturities	(5,677,000)	(5,676,000)	(7,650,000)
Long-term debt	1,072,850,000	1,042,183,000	1,127,178,000
6.6% Senior Notes, Due 2018
Debt Instrument
Total debt	298,730,000	298,677,000	298,525,000
7% Debentures, Due 2025
Debt Instrument
Total debt	124,450,000	124,443,000	124,424,000
6.25% Senior Notes, Due 2037
Debt Instrument
Total debt	228,122,000	228,114,000	228,089,000
Term Loan Facility, Due 2015
Debt Instrument
Total debt	240,000,000	245,000,000	245,000,000
Revolving Facility
Debt Instrument
Credit Facility	110,000,000	50,000,000	135,000,000
AR Credit Facility
Debt Instrument
Credit Facility	75,600,000	100,000,000	100,000,000
Other notes
Debt Instrument
Other notes	$ 1,625,000	$ 1,625,000	$ 3,790,000