Revenue - Schedule of Net Sales Disaggregates by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 03, 2020	Sep. 28, 2019	Oct. 03, 2020	Sep. 28, 2019
Revenue from Contract with Customers [Line Items]
Revenues	$ 4,927,960	$ 5,464,502	$ 14,879,603	$ 17,457,112
Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,256,537	1,513,884	3,899,970	5,071,027
Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	957,216	979,082	2,830,936	3,173,289
Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	362,192	378,670	1,159,949	1,214,355
Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	266,680	372,837	985,001	1,438,651
Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	274,915	296,519	830,283	919,711
Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	463,286	469,180	1,300,518	1,249,912
Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	999,803	1,054,660	2,857,225	3,055,441
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	347,331	399,670	1,015,721	1,334,726
Steel Mills [Member]
Revenue from Contract with Customers [Line Items]
Revenues	2,842,625	3,244,473	8,875,856	10,897,322
Steel Mills [Member] | Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,256,537	1,513,884	3,899,970	5,071,027
Steel Mills [Member] | Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	957,216	979,082	2,830,936	3,173,289
Steel Mills [Member] | Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	362,192	378,670	1,159,949	1,214,355
Steel Mills [Member] | Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	266,680	372,837	985,001	1,438,651
Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,738,004	1,820,359	4,988,026	5,225,064
Steel Products [Member] | Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	274,915	296,519	830,283	919,711
Steel Products [Member] | Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	463,286	469,180	1,300,518	1,249,912
Steel Products [Member] | Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	999,803	1,054,660	2,857,225	3,055,441
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	347,331	399,670	1,015,721	1,334,726
Raw Materials [Member] | Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	$ 347,331	$ 399,670	$ 1,015,721	$ 1,334,726