Investment in Unconsolidated Affiliate - Schedule of Financial Information of Unconsolidated Affiliates (Detail) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2025	Aug. 31, 2024	May 31, 2025	May 31, 2024
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	$ 78.3	$ 36.0	$ 38.0	$ 40.2
Total assets	2,243.3		1,961.8
Current liabilities	693.6		631.5
Other noncurrent liabilities	48.8		32.8
Equity	1,104.9		1,074.1
Total liabilities, mezzanine equity, and equity	2,243.3		1,961.8
Net sales	872.9	834.0
Gross margin	115.2	100.4
Operating income	48.3	43.4
Depreciation and amortization	20.3	16.2
Income tax expense	13.4	4.0
Net earnings	38.6	32.2
Serviacero Worthington
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	29.3		16.0
Other current assets	225.3		219.4
Noncurrent assets	61.2		62.2
Total assets	315.8		297.6
Current liabilities	46.1		40.5
Other noncurrent liabilities	4.9		5.0
Equity	264.8		252.1
Total liabilities, mezzanine equity, and equity	315.8		$ 297.6
Net sales	134.2	148.5
Gross margin	18.6	15.6
Operating income	14.5	11.7
Depreciation and amortization	1.0	1.1
Interest expense	0.0	0.0
Income tax expense	2.0	6.8
Net earnings	$ 12.8	$ 2.6