Segment Data - Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2021
Segment Reporting Information [Line Items]
Net sales	$ 4,916,392	$ 5,242,219	$ 3,171,429
Capital expenditures	86,366	94,600	82,178
Depreciation and amortization	112,800	98,827	87,654
Restructuring and other (income) expense, net		(445)
Separation costs	24,048
Miscellaneous income (expense), net	(1,227)	2,714	2,163
Equity in net income of unconsolidated affiliates	160,987	213,641	123,325
Adjusted EBIT	345,368	514,286	917,717
Total assets	3,650,918	3,643,023
Steel Processing
Segment Reporting Information [Line Items]
Net sales	3,497,896	3,933,021	2,059,397
Capital expenditures	45,133	35,898	28,306
Depreciation and amortization	66,383	55,771	40,870
Impairment of long-lived assets	2,112	3,076
Restructuring and other (income) expense, net	(4,204)	(14,480)	1,883
Miscellaneous income (expense), net	3,270	862	(371)
Equity in net income of unconsolidated affiliates	7,725	29,787	15,965
Adjusted EBIT	121,686	203,272	208,175
Total assets	1,758,981	2,082,522
Consumer products
Segment Reporting Information [Line Items]
Net sales	686,319	636,478	523,697
Capital expenditures	13,635	13,375	13,334
Depreciation and amortization	15,734	10,919	10,145
Impairment of long-lived assets			506
Restructuring and other (income) expense, net	213		41
Miscellaneous income (expense), net	(205)	(76)	(512)
Adjusted EBIT	78,047	94,302	74,936
Total assets	615,430	577,026
Building Products
Segment Reporting Information [Line Items]
Net sales	586,059	541,757	402,038
Capital expenditures	17,819	31,064	22,705
Depreciation and amortization	17,856	18,112	17,321
Impairment of long-lived assets	484		1,423
Restructuring and other (income) expense, net	597	(35)	256
Miscellaneous income (expense), net	349	240	194
Equity in net income of unconsolidated affiliates	166,427	176,498	103,447
Adjusted EBIT	204,611	216,608	117,904
Total assets	635,650	681,188
Sustainable Energy Solutions
Segment Reporting Information [Line Items]
Net sales	146,118	130,954	134,890
Capital expenditures	6,495	6,445	8,652
Depreciation and amortization	6,319	6,554	6,699
Restructuring and other (income) expense, net		(143)	10,293
Miscellaneous income (expense), net	199	64	203
Adjusted EBIT	917	(6,236)	4,961
Total assets	129,872	114,084
Other
Segment Reporting Information [Line Items]
Net sales		9	51,407
Capital expenditures	3,284	7,818	9,181
Depreciation and amortization	6,508	7,471	12,619
Impairment of long-lived assets			11,810
Restructuring and other (income) expense, net	(1,177)	(2,438)	43,624
Separation costs	24,048
Incremental expenses related to Nikola gains			50,624
Miscellaneous income (expense), net	(4,840)	1,624	2,649
Equity in net income of unconsolidated affiliates	(13,165)	7,356	3,913
Adjusted EBIT	(3,199)	8,564	(10,505)
Total assets	510,985	188,203
Consolidated
Segment Reporting Information [Line Items]
Net sales	4,916,392	5,242,219	3,171,429
Capital expenditures	86,366	94,600	82,178
Depreciation and amortization	112,800	98,827	87,654
Impairment of long-lived assets	2,596	3,076	13,739
Restructuring and other (income) expense, net	(4,571)	(17,096)	56,097
Separation costs	24,048
Incremental expenses related to Nikola gains			50,624
Miscellaneous income (expense), net	(1,227)	2,714	2,163
Equity in net income of unconsolidated affiliates	160,987	213,641	123,325
Adjusted EBIT	$ 402,062	$ 516,510	$ 395,471