Long-Term Debt (Tables)

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Long-Term Debt

	June 30,			December 31,			June 30,
	2018			2017			2017
	(Dollars in Thousands)
6.60% Senior Notes, due 2018	$	—		$	299,871		$	299,676
7% Debentures, due 2025		124,225			124,180			124,134
6.25% Senior Notes, due 2037		228,063			228,033			228,003
4.25% Senior Notes, due 2024		396,104			395,814			395,532
4.250% Senior Notes, due 2047		591,457			591,688			—
3.500% Senior Notes, due 2027		494,522			494,352			—
3.450% Senior Notes, due 2027		296,783			296,628			296,456
Floating Rate Senior Notes, due 2019, interest rate of 2.82%    and 2.13% at June 30, 2018 and December 31, 2017,    respectively		298,889			298,102			—
Floating Rate Notes, due 2020, interest rate of 2.98%, 2.10% and    1.82% at June 30, 2018, December 31, 2017 and June 30, 2017,    respectively		298,590			298,227			297,847
Revolving Facility, due 2022, interest rate of 3.19% at June 30, 2018		170,000			—			—
Trade Receivable Facility, interest rate of 2.71% and 1.78% at    June 30, 2018 and 2017, respectively		320,000			—			140,000
Other notes		289			308			333
Total debt		3,218,922			3,027,203			1,781,981
Less: Current maturities of long-term debt and short-term    facilities		(320,046	)		(299,909	)		(140,037	)
Long-term debt	$	2,898,876		$	2,727,294		$	1,641,944