Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 5,170,117	$ 4,290,236	$ 15,160,065	$ 12,251,584
Earnings (loss) before income taxes and noncontrolling interests	370,605	484,172	1,427,716	1,043,619
Total assets	16,503,834		16,503,834		$ 15,223,518
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	3,639,488	2,960,642	10,982,636	8,611,553
Earnings (loss) before income taxes and noncontrolling interests	432,718	591,799	1,734,245	1,402,898
Total assets	9,272,209		9,272,209		8,084,773
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	1,089,519	1,011,602	2,919,992	2,763,335
Earnings (loss) before income taxes and noncontrolling interests	59,225	72,578	131,956	197,891
Total assets	2,893,703		2,893,703		2,544,344
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	441,110	317,992	1,257,437	876,696
Earnings (loss) before income taxes and noncontrolling interests	9,957	14,313	102,575	(76,240)
Total assets	3,462,340		3,462,340		3,235,237
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales	767,268	567,854	2,189,123	1,592,512
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales	28,537	31,117	80,652	80,277
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales	2,333,840	1,774,538	6,971,831	4,717,370
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales	(3,129,645)	(2,373,509)	(9,241,606)	(6,390,159)
Earnings (loss) before income taxes and noncontrolling interests	(131,295)	$ (194,518)	(541,060)	$ (480,930)
Total assets	$ 875,582		$ 875,582		$ 1,359,164