Revenue Recognition - Revenue by Product Class and Timing (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2026	Feb. 28, 2025	Feb. 28, 2026	Feb. 28, 2025
Disaggregation Of Revenue [Line Items]
Net sales	$ 769.8	$ 687.4	$ 2,514.6	$ 2,260.4
Direct | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	743.0	653.8	2,426.6	2,144.6
Toll | Steel Processing
Disaggregation Of Revenue [Line Items]
Net sales	$ 26.8	$ 33.6	$ 88.0	$ 115.8