Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Feb. 28, 2019	Feb. 28, 2019
Disaggregation Of Revenue [Line Items]
Net sales	$ 874,381	$ 2,820,714
Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	825,921	2,676,795
Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	48,460	143,919
Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	555,871	1,851,401
Steel Processing | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	527,970	1,756,842
Steel Processing | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	27,901	94,559
Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	290,690	885,490
Pressure Cylinders | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	270,131	836,130
Pressure Cylinders | Goods and services transferred over time
Disaggregation Of Revenue [Line Items]
Net sales	20,559	49,360
Engineered Cabs
Disaggregation Of Revenue [Line Items]
Net sales	27,817	83,798
Engineered Cabs | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	27,817	83,798
Other
Disaggregation Of Revenue [Line Items]
Net sales	3	25
Other | Goods transferred at a point in time
Disaggregation Of Revenue [Line Items]
Net sales	3	25
Direct
Disaggregation Of Revenue [Line Items]
Net sales	527,970	1,756,842
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	527,970	1,756,842
Toll
Disaggregation Of Revenue [Line Items]
Net sales	27,901	94,559
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	27,901	94,559
Industrial products
Disaggregation Of Revenue [Line Items]
Net sales	148,018	452,883
Industrial products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	148,018	452,883
Consumer products
Disaggregation Of Revenue [Line Items]
Net sales	118,006	352,023
Consumer products | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	118,006	352,023
Oil & gas equipment
Disaggregation Of Revenue [Line Items]
Net sales	24,666	80,584
Oil & gas equipment | Pressure Cylinders
Disaggregation Of Revenue [Line Items]
Net sales	$ 24,666	$ 80,584