Segments - Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 5,131,746	$ 5,464,502	$ 5,895,986	$ 6,096,624	$ 6,295,884	$ 6,742,202	$ 6,460,774	$ 5,568,419	$ 22,588,858	$ 25,067,279	$ 20,252,393
Depreciation expense									648,911	630,879	635,833
Amortization expense									85,742	88,758	91,228
Earnings (loss) before income taxes and noncontrolling interests									1,782,807	3,229,391	1,749,957
Total assets	18,344,666				17,920,588				18,344,666	17,920,588	15,841,258
Capital expenditures									1,512,070	997,256	507,074
Operating Segments [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales									13,933,950	16,245,218	12,929,709
Depreciation expense									401,609	378,146	377,210
Amortization expense									8,624	9,400	9,706
Earnings (loss) before income taxes and noncontrolling interests									1,790,694	3,500,085	1,953,075
Total assets	9,283,216				9,244,086				9,283,216	9,244,086	7,671,217
Capital expenditures									1,133,089	720,310	336,760
Operating Segments [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales									6,990,064	6,796,501	5,579,744
Depreciation expense									85,276	80,681	76,992
Amortization expense									49,914	51,997	52,597
Earnings (loss) before income taxes and noncontrolling interests									511,145	467,105	337,978
Total assets	4,610,628				4,734,636				4,610,628	4,734,636	4,323,907
Capital expenditures									93,848	88,585	90,952
Operating Segments [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales									1,664,844	2,025,560	1,742,940
Depreciation expense									151,124	161,666	172,699
Amortization expense									27,204	27,361	28,925
Earnings (loss) before income taxes and noncontrolling interests									(28,244)	236,241	129,296
Total assets	3,316,479				3,492,126				3,316,479	3,492,126	3,396,110
Capital expenditures									244,818	169,926	59,036
Intercompany Eliminations [Member] | Steel Mills [Member]
Segment Reporting Information [Line Items]
Net sales									3,304,437	3,924,160	2,916,017
Intercompany Eliminations [Member] | Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales									233,728	207,003	118,249
Intercompany Eliminations [Member] | Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales									8,784,397	11,460,645	9,191,081
Corporate and Eliminations Items [Member]
Segment Reporting Information [Line Items]
Net sales									(12,322,562)	(15,591,808)	(12,225,347)
Earnings (loss) before income taxes and noncontrolling interests									(490,788)	(974,040)	(670,392)
Total assets	$ 1,134,343				$ 449,740				1,134,343	449,740	450,024
Corporate [Member]
Segment Reporting Information [Line Items]
Depreciation expense									10,902	10,386	8,932
Capital expenditures									$ 40,315	$ 18,435	$ 20,326