Revenue Recognition - Revenue by Product Class and Over Time (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Disaggregation Of Revenue [Line Items]
Net sales	$ 827,637	$ 958,226	$ 1,683,496	$ 1,946,333
Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	63,410	50,515	123,147	95,459
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	516,937	635,043	1,040,312	1,295,530
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	290,136	294,447	594,532	594,800
Other
Disaggregation Of Revenue [Line Items]
Net sales	20,564	28,736	48,652	56,003
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	481,058	602,010	974,704	1,228,872
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	35,879	33,033	65,608	66,658
Toll | Steel Processing | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	35,879	33,033	65,608	66,658
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	130,334	152,018	282,952	304,865
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	128,065	117,194	247,545	234,017
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	31,737	25,235	64,035	55,918
Engineered Cabs | Other
Disaggregation Of Revenue [Line Items]
Net sales	20,550	28,729	48,616	55,981
Other | Other
Disaggregation Of Revenue [Line Items]
Net sales	14	7	36	22
Certain oil & gas contracts | Pressure Cylinders | Over time revenue
Disaggregation Of Revenue [Line Items]
Net sales	$ 27,531	$ 17,482	$ 57,539	$ 28,801