Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Nov. 30, 2021	Nov. 30, 2020	Nov. 30, 2021	Nov. 30, 2020
Disaggregation Of Revenue [Line Items]
Net sales		$ 1,232,861	$ 731,092	$ 2,343,679	$ 1,434,001
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales		37,176	39,534	71,958	73,445
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales		937,842	468,723	1,760,652	899,743
Other
Disaggregation Of Revenue [Line Items]
Net sales			16,844		39,151
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales		900,666	433,556	1,688,694	838,364
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales		37,176	35,167	71,958	61,379
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales		37,176	35,167	71,958	61,379
Building Products
Disaggregation Of Revenue [Line Items]
Net sales	[1]	121,125	93,989	235,868	182,092
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	[1]	140,793	117,513	288,576	251,135
Sustainable Energy Solutions
Disaggregation Of Revenue [Line Items]
Net sales	[1]	$ 33,101	34,023	$ 58,583	61,880
Oil & gas equipment | Other
Disaggregation Of Revenue [Line Items]
Net sales			6,646		16,542
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales			84		1,070
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales			10,114		21,539
Certain oil & gas equipment contracts | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales			$ 4,367		$ 12,066

[1] The products contained within each of these reportable segments have similar production processes, require substantially the same raw materials, use similar equipment and serve similar purposes. Therefore, we believe the products within each of these segments are appropriately combined for purposes of the disclosure requirements prescribed by ASC 280 and ASC 606.  See NOTE O - Segment Operations for information regarding the reorganization of our pressure cylinders business and the resulting new reportable segments, effective June 1, 2021.