Investments - Schedule of Financial Information of Unconsolidated Affiliates (Detail) - USD ($)	3 Months Ended				9 Months Ended
	Feb. 28, 2026	Feb. 28, 2025	Nov. 30, 2024	Aug. 31, 2024	Feb. 28, 2026	Feb. 28, 2025	May 31, 2025	May 31, 2024
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	$ 90,000,000	$ 63,300,000			$ 90,000,000	$ 63,300,000	$ 38,000,000	$ 40,200,000
Total assets	2,315,500,000				2,315,500,000		1,961,800,000
Current liabilities	745,600,000				745,600,000		631,500,000
Other noncurrent liabilities	57,300,000				57,300,000		32,800,000
Equity	1,124,500,000				1,124,500,000		1,074,100,000
Total liabilities, mezzanine equity, and equity	2,315,500,000				2,315,500,000		1,961,800,000
Net sales	769,800,000	687,400,000			2,514,600,000	2,260,400,000
Gross margin	76,100,000	81,200,000			284,500,000	261,600,000
Operating income	3,100,000	18,300,000			73,100,000	80,600,000
Depreciation and amortization					63,600,000	49,100,000
Interest expense	200,000	0			200,000	0
Income tax expense (benefit)	3,500,000	5,000,000			21,100,000	12,600,000
Net earnings	10,800,000	12,100,000	$ 16,100,000	$ 32,200,000	70,900,000	60,400,000
Serviacero Worthington
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	54,900,000				54,900,000		16,000,000
Other current assets	195,000,000				195,000,000		219,400,000
Noncurrent assets	61,700,000				61,700,000		62,200,000
Total assets	311,600,000				311,600,000		297,600,000
Current liabilities	33,400,000				33,400,000		40,500,000
Other noncurrent liabilities	4,800,000				4,800,000		5,000,000
Equity	273,400,000				273,400,000		252,100,000
Total liabilities, mezzanine equity, and equity	311,600,000				311,600,000		$ 297,600,000
Net sales	99,700,000	99,700,000			370,500,000	386,900,000
Gross margin	11,600,000	8,200,000			48,400,000	33,400,000
Operating income	7,300,000	4,300,000			36,200,000	21,500,000
Depreciation and amortization	1,100,000	1,200,000			3,100,000	3,500,000
Interest expense	0	0			0	0
Income tax expense (benefit)	(800,000)	200,000			1,900,000	12,800,000
Net earnings	$ 7,000,000	$ 0			$ 33,300,000	$ 900,000