Segment Operations - Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands		3 Months Ended
		Aug. 31, 2021	Aug. 31, 2020	May 31, 2021
Segment Reporting Information [Line Items]
Net sales		$ 1,110,818	$ 702,909
Operating income (loss)		135,797	(30,121)
Impairment of long-lived assets		0	9,924
Restructuring and other (income) expense, net		(12,274)	1,848
Equity in net income of unconsolidated affiliates		52,916	23,634
Less net earnings attributable to noncontrolling interests		8,984	2,063
Adjusted earnings (loss) before interest and taxes		181,625	782,516
Total assets		3,547,755		$ 3,373,245
Steel Processing
Segment Reporting Information [Line Items]
Net sales		822,810	431,020
Operating income (loss)		113,482	13,617
Restructuring and other (income) expense, net		(12,131)	1,471
Adjusted operating income (loss)		101,351	15,088
Miscellaneous income (loss), net		30	(43)
Equity in net income of unconsolidated affiliates		9,349	1,309
Less net earnings attributable to noncontrolling interests	[1]	3,038	2,179
Adjusted earnings (loss) before interest and taxes		107,692	14,175
Total assets		1,762,053		1,359,598
Consumer products
Segment Reporting Information [Line Items]
Net sales		147,783	133,622
Operating income (loss)		20,506	23,424
Impairment of long-lived assets			506
Adjusted operating income (loss)		20,506	23,930
Miscellaneous income (loss), net		49	(21)
Adjusted earnings (loss) before interest and taxes		20,555	23,909
Total assets		550,712		541,028
Building Products
Segment Reporting Information [Line Items]
Net sales		114,743	88,103
Operating income (loss)		5,834	(440)
Impairment of long-lived assets			1,423
Adjusted operating income (loss)		5,834	983
Miscellaneous income (loss), net		(73)	(161)
Equity in net income of unconsolidated affiliates		42,993	22,552
Adjusted earnings (loss) before interest and taxes		48,754	23,374
Total assets		574,077		664,113
Sustainable Energy Solutions
Segment Reporting Information [Line Items]
Net sales		25,482	27,857
Operating income (loss)		(2,352)	(643)
Restructuring and other (income) expense, net		(143)
Adjusted operating income (loss)		(2,495)	(643)
Miscellaneous income (loss), net		(59)	82
Adjusted earnings (loss) before interest and taxes		(2,554)	(561)
Total assets		114,788		169,550
Other
Segment Reporting Information [Line Items]
Net sales			22,307
Operating income (loss)		(1,673)	(66,079)
Impairment of long-lived assets			7,995
Restructuring and other (income) expense, net			377
Incremental expenses related to Nikola gains			49,511
Adjusted operating income (loss)		(1,673)	(8,196)
Miscellaneous income (loss), net		683	595
Equity in net income of unconsolidated affiliates		574	(227)
Adjusted earnings (loss) before interest and taxes		(416)	(7,828)
Total assets		546,125		$ 638,956
Consolidated
Segment Reporting Information [Line Items]
Net sales		1,110,818	702,909
Operating income (loss)		135,797	(30,121)
Impairment of long-lived assets			9,924
Restructuring and other (income) expense, net		(12,274)	1,848
Incremental expenses related to Nikola gains			49,511
Adjusted operating income (loss)		123,523	31,162
Miscellaneous income (loss), net		630	452
Equity in net income of unconsolidated affiliates		52,916	23,634
Less net earnings attributable to noncontrolling interests	[1]	3,038	2,179
Adjusted earnings (loss) before interest and taxes		$ 174,031	$ 53,069

[1] Excludes the noncontrolling interest portion of impairment and restructuring charges (gains) of $(5,946,000) and $116,000 for the three months ended August 31, 2021 and 2020, respectively