Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019
Disaggregation Of Revenue [Line Items]
Net sales	$ 731,092	$ 827,637	$ 1,434,001	$ 1,683,496
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	39,534	63,410	73,445	123,147
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	468,723	516,937	899,743	1,040,312
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	262,284	290,136	533,188	594,532
Other
Disaggregation Of Revenue [Line Items]
Net sales	85	20,564	1,070	48,652
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	433,556	481,058	838,364	974,704
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	35,167	35,879	61,379	65,608
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	35,167	35,879	61,379	65,608
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	134,020	130,334	262,245	282,952
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	121,618	128,065	254,400	247,545
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	6,646	31,737	16,543	64,035
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales	85	20,550	1,070	48,616
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales		14		36
Certain oil & gas equipment contracts | Pressure Cylinders | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	$ 4,367	$ 27,531	$ 12,066	$ 57,539