Debt and Other Financing Arrangements (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Debt and Other Financing Arrangements

	(in thousands) December 31,
	2017		2016
Industrial revenue bonds due from 2020 to 2040*	$	1,010,600	$	1,010,600
Notes, 5.75%, due 2017		—		600,000
Notes, 5.85%, due 2018		500,000		500,000
Notes, 4.125%, due 2022		600,000		600,000
Notes, 4.0%, due 2023		500,000		500,000
Notes, 6.40%, due 2037		650,000		650,000
Notes, 5.20%, due 2043		500,000		500,000
Total long-term debt		3,760,600		4,360,600
Less debt issuance costs		18,358		21,459
Total amounts outstanding		3,742,242		4,339,141
Less current maturities		500,000		600,000
Total long-term debt due after one year	$	3,242,242	$	3,739,141

* The industrial revenue bonds had variable rates ranging from 1.65% to 1.92% and 0.79% to 1.00% at

December 31, 2017 and 2016, respectively.