Long-Term Debt (Tables)

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Long-Term Debt

	March 31,			December 31,			March 31,
	2018			2017			2017
	(Dollars in Thousands)
6.60% Senior Notes, due 2018	$	299,967		$	299,871		$	299,579
7% Debentures, due 2025		124,203			124,180			124,112
6.25% Senior Notes, due 2037		228,048			228,033			227,989
4.25% Senior Notes, due 2024		395,959			395,814			395,392
4.250% Senior Notes, due 2047		591,416			591,688			—
3.500% Senior Notes, due 2027		494,402			494,352			—
3.450% Senior Notes, due 2027		296,705			296,628			—
Floating Rate Senior Notes, due 2019, interest rate of 2.70%    and 2.13% at March 31, 2018 and December 31, 2017,    respectively		298,704			298,102			—
Floating Rate Notes, due 2020, interest rate of 2.55% and 2.10%    at March 31, 2018 and December 31, 2017, respectively		298,408			298,227			—
Floating Rate Notes, due 2017, interest rate of 2.10% at    March 31, 2017		—			—			298,878
Revolving Facility, due 2022, interest rate of 1.89% at March 31,    2017		—			—			210,000
Trade Receivable Facility, interest rate of 1.51% at March 31,    2017		—			—			290,000
Other notes		296			308			344
Total debt		3,028,108			3,027,203			1,846,294
Less: Current maturities of long-term debt and short-term    facilities		(300,006	)		(299,909	)		(290,048	)
Long-term debt	$	2,728,102		$	2,727,294		$	1,556,246