Investment in Unconsolidated Affiliate - Schedule of Combined Financial Information of Unconsolidated Affiliates (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Nov. 30, 2023	Aug. 31, 2023	Nov. 30, 2022	Aug. 31, 2022	Nov. 30, 2023	Nov. 30, 2022	May 31, 2023
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	$ 214.4				$ 214.4		$ 32.7
Total assets	1,897.4				1,897.4		1,764.4
Current liabilities	595.3				595.3		478.4
Short-term borrowings	175.0				175.0		2.8
Current maturities of long-term debt	20.0				20.0		20.0
Other noncurrent liabilities	34.6				34.6		33.6
Equity	1,040.3				1,040.3		1,029.0
Total liabilities and equity	1,897.4				1,897.4		1,764.4
Net sales	808.0		$ 868.4		1,713.8	$ 1,943.0
Gross margin	60.2		34.5		188.7	123.1
Operating income	(8.8)		(19.9)		60.9	21.0
Depreciation and amortization	16.4		17.8		33.3	35.5
Income tax expense	(2.5)		(5.5)		14.5	4.8
Net earnings (loss)	(2.1)	$ 62.1	(12.5)	$ 31.3	60.0	18.8
Serviacero Worthington
Investments in and Advances to Affiliates [Line Items]
Cash and cash equivalents	2.9				2.9		12.2
Other current assets	283.8				283.8		238.2
Noncurrent assets	57.2				57.2		58.9
Total assets	343.9				343.9		309.3
Current liabilities	85.1				85.1		70.8
Other noncurrent liabilities	5.3				5.3		5.4
Equity	253.5				253.5		233.1
Total liabilities and equity	343.9				343.9		$ 309.3
Net sales	163.4		157.4		315.3	320.0
Gross margin	18.6		6.9		39.9	16.0
Operating income	15.2		4.1		33.1	10.5
Depreciation and amortization	1.1		1.1		2.1	2.2
Interest expense	0.0		0.1		0.0	0.1
Income tax expense	6.3		0.8		7.0	2.6
Net earnings (loss)	$ 7.6		$ 3.8		$ 25.5	$ 7.4