Revenue - Schedule of Net Sales Disaggregates by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Revenue from Contract with Customers [Line Items]
Revenues	$ 5,895,986	$ 6,460,774	$ 11,992,610	$ 12,029,193
Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,749,840	1,974,427	3,557,143	3,640,647
Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,079,077	1,258,438	2,194,207	2,348,585
Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	401,756	448,557	835,685	845,254
Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	472,774	488,117	1,065,814	915,747
Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	293,321	371,568	623,192	682,796
Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	438,677	390,921	780,732	720,140
Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,018,185	975,881	2,000,781	1,804,145
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	442,356	552,865	935,056	1,071,879
Steel Mills [Member]
Revenue from Contract with Customers [Line Items]
Revenues	3,703,447	4,169,539	7,652,849	7,750,233
Steel Mills [Member] | Sheet [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,749,840	1,974,427	3,557,143	3,640,647
Steel Mills [Member] | Bar [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,079,077	1,258,438	2,194,207	2,348,585
Steel Mills [Member] | Structural [Member]
Revenue from Contract with Customers [Line Items]
Revenues	401,756	448,557	835,685	845,254
Steel Mills [Member] | Plate [Member]
Revenue from Contract with Customers [Line Items]
Revenues	472,774	488,117	1,065,814	915,747
Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,750,183	1,738,370	3,404,705	3,207,081
Steel Products [Member] | Tubular Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	293,321	371,568	623,192	682,796
Steel Products [Member] | Rebar Fabrication [Member]
Revenue from Contract with Customers [Line Items]
Revenues	438,677	390,921	780,732	720,140
Steel Products [Member] | Other Steel Products [Member]
Revenue from Contract with Customers [Line Items]
Revenues	1,018,185	975,881	2,000,781	1,804,145
Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	442,356	552,865	935,056	1,071,879
Raw Materials [Member] | Raw Materials [Member]
Revenue from Contract with Customers [Line Items]
Revenues	$ 442,356	$ 552,865	$ 935,056	$ 1,071,879