Segments - Schedule of Net Sale by Product to External Customers (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 to external customers	$ 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
Sheet [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									6,450,506	7,571,765	6,407,974
Bar [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									4,106,640	4,709,292	3,558,806
Structural [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,573,248	1,830,476	1,317,995
Plate [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,803,556	2,133,685	1,644,934
Tubular Products [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,207,398	1,347,577	917,235
Rebar Fabrication [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									1,666,445	1,496,194	1,306,418
Other Steel Products [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									4,116,221	3,952,730	3,356,091
Raw Materials [Member]
Segment Reporting Information [Line Items]
Net sales to external customers									$ 1,664,844	$ 2,025,560	$ 1,742,940