Revenue Recognition - Disaggregation of Revenue by Product Class and Timing (Detail) $ in Thousands	3 Months Ended
	Aug. 31, 2018 USD ($)
Disaggregation Of Revenue [Line Items]
Net sales	$ 988,107
Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	943,163
Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	44,944
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	660,487
Steel Processing | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	626,862
Steel Processing | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	33,625
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	300,353
Pressure Cylinders | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	289,034
Pressure Cylinders | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	11,319
Engineered Cabs
Disaggregation Of Revenue [Line Items]
Net sales	27,252
Engineered Cabs | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	27,252
Other
Disaggregation Of Revenue [Line Items]
Net sales	15
Other | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	15
Direct
Disaggregation Of Revenue [Line Items]
Net sales	626,862
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	626,862
Toll
Disaggregation Of Revenue [Line Items]
Net sales	33,625
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	33,625
Industrial products
Disaggregation Of Revenue [Line Items]
Net sales	152,847
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	152,847
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	116,823
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	116,823
Oil & gas equipment
Disaggregation Of Revenue [Line Items]
Net sales	30,683
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	$ 30,683