Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2022	May 31, 2021	May 31, 2020
Disaggregation Of Revenue [Line Items]
Net sales	$ 5,242,219	$ 3,171,429	$ 3,059,119
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	144,732	147,645	230,472
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	3,933,021	2,059,397	1,859,670
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	3,788,289	1,927,418	1,729,972
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	144,732	131,979	129,698
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	144,732	131,979	129,698
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	636,478	523,697	449,337
Building Products
Disaggregation Of Revenue [Line Items]
Net sales	541,757	402,038	383,372
Sustainable Energy Solutions
Disaggregation Of Revenue [Line Items]
Net sales	130,954	134,890	122,113
Oil & gas contracts | Other
Disaggregation Of Revenue [Line Items]
Net sales		20,950	111,891
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales		1,058	50,954
Other
Disaggregation Of Revenue [Line Items]
Net sales	9	51,407	244,627
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales	$ 9	29,399	81,782
Certain oil & gas contracts | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales		$ 15,666	$ 100,774