Revenue Recognition - Revenue by Product Class and Timing (Detail) $ in Thousands	12 Months Ended
	May 31, 2019 USD ($)
Disaggregation Of Revenue [Line Items]
Net sales	$ 3,759,556
Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	3,557,335
Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	202,221
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	2,435,818
Steel Processing | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	2,308,756
Steel Processing | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	127,062
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	1,207,798
Pressure Cylinders | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	1,132,639
Pressure Cylinders | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	75,159
Engineered Cabs
Disaggregation Of Revenue [Line Items]
Net sales	115,902
Engineered Cabs | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	115,902
Other
Disaggregation Of Revenue [Line Items]
Net sales	38
Other | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	38
Direct
Disaggregation Of Revenue [Line Items]
Net sales	2,308,756
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	2,308,756
Toll
Disaggregation Of Revenue [Line Items]
Net sales	127,062
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	127,062
Industrial products
Disaggregation Of Revenue [Line Items]
Net sales	627,053
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	627,053
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	470,447
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	470,447
Oil & gas equipment
Disaggregation Of Revenue [Line Items]
Net sales	110,298
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	$ 110,298