Long-Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Debt Instrument [Line Items]
Total debt	$ 1,764,835	$ 1,568,774	$ 1,700,771
Less: Current maturities	(228,025)	(18,713)	(147,003)
Long-term debt	1,536,810	1,550,061	1,553,768
6.6% Senior Notes, Due 2018
Debt Instrument [Line Items]
Total debt	299,388	299,113	299,020
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124,068	124,002	123,981
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	227,961	227,917	227,907
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	395,115	394,690	394,575
Floating Rate Notes, Due 2017
Debt Instrument [Line Items]
Total debt	298,750	298,868	298,731
Term Loan Facility, Due 2018
Debt Instrument [Line Items]
Total debt	209,096	222,521	225,433
Trade Receivable Facility
Debt Instrument [Line Items]
Total debt	210,000		130,000
Other Notes
Debt Instrument [Line Items]
Total debt	$ 457	$ 1,663	$ 1,124