Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jul. 04, 2015	Jul. 02, 2016	Jul. 04, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 4,245,772	$ 4,357,609	$ 7,961,348	$ 8,757,049
Earnings (loss) before income taxes and noncontrolling interests	370,884	216,222	512,410	335,267
Total assets	14,924,583		14,924,583		$ 14,226,944
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,016,322	2,968,644	5,650,911	6,021,983
Earnings (loss) before income taxes and noncontrolling interests	530,727	198,500	810,562	415,628
Total assets	7,667,489		7,667,489		7,318,706
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	923,357	1,015,646	1,751,733	1,937,030
Earnings (loss) before income taxes and noncontrolling interests	82,946	70,636	125,313	103,094
Total assets	2,538,141		2,538,141		2,485,122
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	306,093	373,319	558,704	798,036
Earnings (loss) before income taxes and noncontrolling interests	(27,181)	(38,104)	(90,553)	(79,601)
Total assets	3,200,209		3,200,209		3,123,190
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(2,353,819)	(2,286,232)	(4,016,650)	(4,713,630)
Earnings (loss) before income taxes and noncontrolling interests	(215,608)	(14,810)	(332,912)	(103,854)
Total assets	1,518,744		1,518,744		$ 1,299,926
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	554,395	577,271	1,024,658	1,152,254
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	27,954	21,020	49,160	40,517
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	$ 1,771,470	$ 1,687,941	$ 2,942,832	$ 3,520,859