Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2021
Disaggregation Of Revenue [Line Items]
Net sales	$ 4,916,392	$ 5,242,219	$ 3,171,429
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	140,781	144,732	147,645
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	3,497,896	3,933,021	2,059,397
Other
Disaggregation Of Revenue [Line Items]
Net sales		9	51,407
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	3,357,115	3,788,289	1,927,418
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	140,781	144,732	131,979
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	140,781	144,732	131,979
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	686,319	636,478	523,697
Building Products
Disaggregation Of Revenue [Line Items]
Net sales	586,059	541,757	402,038
Sustainable Energy Solutions
Disaggregation Of Revenue [Line Items]
Net sales	$ 146,118	130,954	134,890
Oil & Gas Equipment | Other
Disaggregation Of Revenue [Line Items]
Net sales			20,950
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales			1,058
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales		$ 9	29,399
Certain oil & gas contracts | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales			$ 15,666