Segment Operations - Financial Information for Reportable Segments (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Feb. 28, 2022		Feb. 28, 2021		Feb. 28, 2022		Feb. 28, 2021		May 31, 2021
Segment Reporting Information [Line Items]
Net sales		$ 1,378,235		$ 759,109		$ 3,721,914		$ 2,193,110
Impairment of long-lived assets		3,076		0		3,076		13,739
Restructuring and other (income) expense, net		(504)		28,212		(14,782)		37,656
Equity in net income of unconsolidated affiliates		47,466		31,674		160,600		80,939
Adjusted earnings (loss) before interest and taxes		77,330		77,167		403,366		771,726
Total assets		3,738,160				3,738,160				$ 3,373,245
Steel Processing
Segment Reporting Information [Line Items]
Net sales		1,052,562		504,477		2,813,214		1,404,220
Impairment of long-lived assets		3,076				3,076
Restructuring and other (income) expense, net		114	[1]	(42)	[1]	(12,199)	[2]	1,804	[2]
Miscellaneous income (loss), net		(12)		(196)		35		(244)
Equity in net income of unconsolidated affiliates		4,692		4,223		22,864		7,393
Adjusted earnings (loss) before interest and taxes		7,116		61,789		186,734		110,345
Total assets		2,245,260				2,245,260				1,359,598
Consumer products
Segment Reporting Information [Line Items]
Net sales		161,692		115,071		450,268		366,205
Impairment of long-lived assets	[2]							506
Restructuring and other (income) expense, net	[2]							120
Miscellaneous income (loss), net		(39)		(132)		169		(249)
Adjusted earnings (loss) before interest and taxes		26,674		14,594		64,813		55,934
Total assets		563,203				563,203				541,028
Building Products
Segment Reporting Information [Line Items]
Net sales		132,944		96,256		368,813		278,349
Impairment of long-lived assets	[2]							1,423
Restructuring and other (income) expense, net		(35)	[1]			(35)	[2]
Miscellaneous income (loss), net		(3)		181		141		89
Equity in net income of unconsolidated affiliates		39,978		25,379		132,865		70,622
Adjusted earnings (loss) before interest and taxes		49,570		27,340		153,042		76,675
Total assets		636,254				636,254				664,113
Sustainable Energy Solutions
Segment Reporting Information [Line Items]
Net sales		31,037		32,103		89,619		93,982
Restructuring and other (income) expense, net	[2]					(143)
Miscellaneous income (loss), net		(38)		42		(16)		194
Adjusted earnings (loss) before interest and taxes		(2,801)		131		(4,561)		1,106
Total assets		119,073				119,073				169,550
Other
Segment Reporting Information [Line Items]
Net sales				11,202				50,354
Impairment of long-lived assets	[2]							11,810
Restructuring and other (income) expense, net		(583)	[1]	28,254	[1]	(2,405)	[2]	35,732	[2]
Miscellaneous income (loss), net		485		644		1,734		1,576
Incremental expenses related to Nikola gains				(781)				53,300
Equity in net income of unconsolidated affiliates		2,796		2,072		4,871		2,924
Adjusted earnings (loss) before interest and taxes		4,039		492		5,517		(12,968)
Total assets		174,370				174,370				$ 638,956
Consolidated
Segment Reporting Information [Line Items]
Net sales		1,378,235		759,109		3,721,914		2,193,110
Impairment of long-lived assets		3,076				3,076		13,739	[2]
Restructuring and other (income) expense, net		(504)	[1]	28,212	[1]	(14,782)	[2]	37,656	[2]
Miscellaneous income (loss), net		393		539		2,063		1,366
Incremental expenses related to Nikola gains				(781)				53,300
Equity in net income of unconsolidated affiliates		47,466		31,674		160,600		80,939
Adjusted earnings (loss) before interest and taxes		$ 84,598		$ 104,346		$ 405,545		$ 231,092

[1] Includes the noncontrolling interest portion of restructuring (charges) gains of $(1,139) and $3 for the three months ended February 28, 2022 and 2021, respectively

[2] Includes the noncontrolling interest portion of impairment and restructuring (charges) gains of $4,888 and $(255) for the nine months ended February 28, 2022 and 2021, respectively