Segment Operations - Financial Information for Reportable Segments (Detail) - USD ($)		3 Months Ended
		Aug. 31, 2022	Aug. 31, 2021	May 31, 2022
Segment Reporting Information [Line Items]
Net sales		$ 1,408,665,000	$ 1,110,818,000
Impairment of long-lived assets		312,000
Restructuring and other expense (income), net		(1,100,000)	(12,274,000)
Miscellaneous income (expense), net		(5,086,000)	630,000
Equity in net income of unconsolidated affiliates		31,712,000	52,916,000
Adjusted earnings (loss) before interest and taxes		84,742,000	181,625,000
Total assets		3,510,142,000		$ 3,643,023,000
Steel Processing
Segment Reporting Information [Line Items]
Net sales			822,810,000
Restructuring and other expense (income), net			(12,131,000)
Miscellaneous income (expense), net			30,000
Equity in net income of unconsolidated affiliates			9,349,000
Adjusted earnings (loss) before interest and taxes	[1]		107,692,000
Total assets		2,016,113,000		2,082,522,000
Consumer products
Segment Reporting Information [Line Items]
Net sales			147,783,000
Miscellaneous income (expense), net			49,000
Adjusted earnings (loss) before interest and taxes	[1]		20,555,000
Total assets		636,208,000		577,026,000
Building Products
Segment Reporting Information [Line Items]
Net sales			114,743,000
Miscellaneous income (expense), net			(73,000)
Equity in net income of unconsolidated affiliates			42,993,000
Adjusted earnings (loss) before interest and taxes	[1]		48,754,000
Total assets		648,502,000		681,188,000
Sustainable Energy Solutions
Segment Reporting Information [Line Items]
Net sales			25,482,000
Restructuring and other expense (income), net			(143,000)
Miscellaneous income (expense), net			(59,000)
Adjusted earnings (loss) before interest and taxes	[1]		(2,554,000)
Total assets		107,421,000		114,084,000
Other
Segment Reporting Information [Line Items]
Miscellaneous income (expense), net			683,000
Equity in net income of unconsolidated affiliates			574,000
Adjusted earnings (loss) before interest and taxes	[1]		(416,000)
Total assets		$ 101,898,000		$ 188,203,000
Consolidated
Segment Reporting Information [Line Items]
Net sales			1,110,818,000
Restructuring and other expense (income), net			(12,274,000)
Miscellaneous income (expense), net			630,000
Equity in net income of unconsolidated affiliates			52,916,000
Adjusted earnings (loss) before interest and taxes	[1]		$ 174,031,000

[1] Excludes the noncontrolling interest portion of the restructuring gains within Steel Processing of $5,946.