Segments - Schedule of Net Sale by Product to External Customers (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Oct. 03, 2020	Jul. 04, 2020	Apr. 04, 2020	Dec. 31, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales to external customers	$ 5,260,055	$ 4,927,960	$ 4,327,306	$ 5,624,337	$ 5,131,746	$ 5,464,502	$ 5,895,986	$ 6,096,624	$ 20,139,658	$ 22,588,858	$ 25,067,279
Sheet [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									5,450,507	6,450,506	7,571,765
Bar [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									3,821,158	4,106,640	4,709,292
Structural [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,526,283	1,573,248	1,830,476
Plate [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,311,360	1,803,556	2,133,685
Tubular Products [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,113,582	1,207,398	1,347,577
Rebar Fabrication [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,708,442	1,666,445	1,496,194
Other Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									3,801,045	4,116,221	3,952,730
Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									$ 1,407,283	$ 1,664,844	$ 2,025,560