Investments in Unconsolidated Affiliates - Financial Results of Four Largest Unconsolidated Affiliates (Detail) - USD ($) $ in Thousands		12 Months Ended
		May 31, 2020	May 31, 2019	May 31, 2018
Investments In And Advances To Affiliates [Line Items]
Net sales		$ 1,819,996	$ 1,857,811	$ 1,692,019
Gross margin (loss)		376,930	341,278	343,281
Operating income (loss)		223,521	221,549	222,893
Depreciation and amortization		30,519	26,483	25,365
Interest expense		13,992	13,395	10,209
Income tax expense (benefit)		3,453	7,877	5,468
Net earnings (loss)		259,450	209,232	206,976
WAVE
Investments In And Advances To Affiliates [Line Items]
Net sales		368,820	379,103	360,395
Gross margin (loss)		208,040	205,909	201,581
Operating income (loss)		166,404	166,969	158,697
Depreciation and amortization		4,032	3,634	3,318
Interest expense		11,061	10,547	8,365
Income tax expense (benefit)		216	219	119
Net earnings (loss)	[1]	202,451	162,849	152,329
ClarkDietrich
Investments In And Advances To Affiliates [Line Items]
Net sales		855,994	892,758	790,887
Gross margin (loss)		131,619	93,947	97,437
Operating income (loss)		66,952	33,384	39,153
Depreciation and amortization		11,869	11,600	11,864
Interest expense		378	912	114
Net earnings (loss)		68,899	34,560	39,138
Serviacero Worthington
Investments In And Advances To Affiliates [Line Items]
Net sales		273,276	351,671	315,098
Gross margin (loss)		15,739	34,494	32,396
Operating income (loss)		7,513	25,636	24,232
Depreciation and amortization		4,324	4,319	3,919
Interest expense		87	493	397
Income tax expense (benefit)		3,267	7,629	5,141
Net earnings (loss)		2,573	16,155	17,577
ArtiFlex
Investments In And Advances To Affiliates [Line Items]
Net sales		175,428	201,526	197,061
Gross margin (loss)		14,212	12,928	18,266
Operating income (loss)		6,248	5,524	11,395
Depreciation and amortization		5,605	6,055	5,515
Interest expense		801	1,443	1,333
Income tax expense (benefit)		(15)	29	208
Net earnings (loss)		5,461	4,051	9,854
Other [Member]
Investments In And Advances To Affiliates [Line Items]
Net sales		146,478	32,753	28,578
Gross margin (loss)		7,320	(6,000)	(6,399)
Operating income (loss)		(23,596)	(9,964)	(10,584)
Depreciation and amortization		4,689	875	749
Interest expense		1,665
Income tax expense (benefit)		(15)
Net earnings (loss)		$ (19,934)	$ (8,383)	$ (11,922)

[1] These net earnings include net income attributable to discontinued operations of $49,770,000, $6,830,000, and $2,226,000 in fiscal 2020, fiscal 2019, and fiscal 2018, respectively, related to the international operations of WAVE being sold.  All other amounts presented in the table above exclude the activity of the discontinued operations of WAVE.