Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jul. 02, 2016	Jul. 01, 2017	Jul. 02, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 5,174,769	$ 4,245,772	$ 9,989,948	$ 7,961,348
Earnings (loss) before income taxes and noncontrolling interests	508,136	389,884	1,057,111	559,447
Total assets	16,112,725		16,112,725		$ 15,223,518
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,800,359	3,016,322	7,343,148	5,650,911
Earnings (loss) before income taxes and noncontrolling interests	617,366	530,727	1,301,527	811,099
Total assets	9,230,612		9,230,612		8,084,773
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	970,398	923,357	1,830,473	1,751,733
Earnings (loss) before income taxes and noncontrolling interests	45,809	82,946	72,731	125,313
Total assets	2,691,020		2,691,020		2,544,344
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	404,012	306,093	816,327	558,704
Earnings (loss) before income taxes and noncontrolling interests	66,227	(27,181)	92,618	(90,553)
Total assets	3,316,269		3,316,269		3,235,237
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	760,937	554,395	1,421,855	1,024,658
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	24,972	27,954	52,115	49,160
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	2,459,352	1,771,470	4,637,991	2,942,832
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(3,245,261)	(2,353,819)	(6,111,961)	(4,016,650)
Earnings (loss) before income taxes and noncontrolling interests	(221,266)	$ (196,608)	(409,765)	$ (286,412)
Total assets	$ 874,824		$ 874,824		$ 1,359,164