Goodwill and Other Intangible Assets - Schedule of Change in Net Carrying Amount of Goodwill by Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Balance, beginning of period	$ 2,184,336	$ 2,196,058
Acquisitions	12,623
Translation	4,104	(11,722)
Balance, end of period	2,201,063	2,184,336
Steel Mills [Member]
Goodwill [Line Items]
Balance, beginning of period	591,986	745,484
Reclassifications		(153,498)
Balance, end of period	591,986	591,986
Steel Products [Member]
Goodwill [Line Items]
Balance, beginning of period	862,773	720,997
Reclassifications		153,498
Acquisitions	12,623
Translation	4,104	(11,722)
Balance, end of period	879,500	862,773
Raw Materials [Member]
Goodwill [Line Items]
Balance, beginning of period	729,577	729,577
Balance, end of period	$ 729,577	$ 729,577