Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Nov. 30, 2018	Nov. 30, 2018
Disaggregation Of Revenue [Line Items]
Net sales	$ 958,226	$ 1,946,333
Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	907,711	1,850,874
Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	50,515	95,459
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	635,043	1,295,530
Steel Processing | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	602,010	1,228,872
Steel Processing | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	33,033	66,658
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	294,447	594,800
Pressure Cylinders | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	276,965	565,999
Pressure Cylinders | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	17,482	28,801
Engineered Cabs
Disaggregation Of Revenue [Line Items]
Net sales	28,729	55,981
Engineered Cabs | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	28,729	55,981
Other
Disaggregation Of Revenue [Line Items]
Net sales	7	22
Other | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	7	22
Direct
Disaggregation Of Revenue [Line Items]
Net sales	602,010	1,228,872
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	602,010	1,228,872
Toll
Disaggregation Of Revenue [Line Items]
Net sales	33,033	66,658
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	33,033	66,658
Industrial products
Disaggregation Of Revenue [Line Items]
Net sales	152,018	304,865
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	152,018	304,865
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	117,194	234,017
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	117,194	234,017
Oil & gas equipment
Disaggregation Of Revenue [Line Items]
Net sales	25,235	55,918
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	$ 25,235	$ 55,918