Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2020	Aug. 31, 2019
Disaggregation Of Revenue [Line Items]
Net sales	$ 702,909	$ 855,859
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	33,911	59,737
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	431,020	523,375
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	270,904	304,396
Other
Disaggregation Of Revenue [Line Items]
Net sales	985	28,088
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	404,808	493,646
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	26,212	29,729
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	26,212	29,729
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	128,225	152,618
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	132,782	119,480
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	9,897	32,298
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales	985	28,066
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales		22
Certain oil & gas equipment contracts | Pressure Cylinders | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	$ 7,699	$ 30,008