Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2020	May 31, 2019
Disaggregation Of Revenue [Line Items]
Net sales	$ 3,059,119	$ 3,759,556
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	230,472	202,221
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	1,859,670	2,435,818
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	1,148,424	1,207,798
Other
Disaggregation Of Revenue [Line Items]
Net sales	51,025	115,940
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	1,729,972	2,308,756
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	129,698	127,062
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	129,698	127,062
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	550,543	627,053
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	485,990	470,447
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	111,891	110,298
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales	50,954	115,902
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales	71	38
Certain oil & gas contracts | Pressure Cylinders | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	$ 100,774	$ 75,159