Long-Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Total debt	$ 3,209,698	$ 3,027,203	$ 1,722,540
Less: Current maturities of long-term debt and short-term facilities	(380,041)	(299,909)	(80,038)
Long-term debt	2,829,657	2,727,294	1,642,502
Revolving Facility, Due 2022
Debt Instrument [Line Items]
Total debt	100,000
6.60% Senior Notes, Due 2018
Debt Instrument [Line Items]
Total debt		299,871	299,774
7% Debentures, Due 2025
Debt Instrument [Line Items]
Total debt	124,249	124,180	124,157
6.25% Senior Notes, Due 2037
Debt Instrument [Line Items]
Total debt	228,079	228,033	228,018
4.25% Senior Notes, Due 2024
Debt Instrument [Line Items]
Total debt	396,251	395,814	395,673
4.250% Senior Notes, Due 2047
Debt Instrument [Line Items]
Total debt	591,499	591,688
3.500% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	494,643	494,352
Floating Rate Notes, Due 2020
Debt Instrument [Line Items]
Total debt	298,773	298,227	298,046
3.450% Senior Notes, Due 2027
Debt Instrument [Line Items]
Total debt	296,861	296,628	296,551
Floating Rate Notes, Due 2019
Debt Instrument [Line Items]
Total debt	299,074	298,102
Trade Receivable Facility
Debt Instrument [Line Items]
Total debt	380,000		80,000
Other Notes
Debt Instrument [Line Items]
Total debt	$ 269	$ 308	$ 321