Financial Results of Four Largest Unconsolidated Affiliates (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015
Investments in and Advances to Affiliates [Line Items]
Net sales	$ 1,614,743	$ 1,563,388	$ 1,510,180
Gross margin	390,729	361,221	302,006
Operating income (loss)	272,940	247,250	193,531
Depreciation and amortization	27,999	31,103	35,662
Interest expense (income)	8,721	8,469	8,695
Income tax expense (benefit)	17,362	9,040	10,488
Net earnings (loss)	250,748	258,106	178,102
WAVE
Investments in and Advances to Affiliates [Line Items]
Net sales	400,987	393,718	382,451
Gross margin	207,035	207,143	181,102
Operating income (loss)	167,157	172,721	147,603
Depreciation and amortization	4,871	4,120	4,150
Interest expense (income)	7,183	6,635	6,412
Income tax expense (benefit)	5,626	2,449	2,539
Net earnings (loss)	154,866	164,132	138,670
ClarkDietrich
Investments in and Advances to Affiliates [Line Items]
Net sales	711,735	615,609	576,171
Gross margin	128,098	95,427	65,530
Operating income (loss)	68,696	33,897	10,436
Depreciation and amortization	12,718	14,289	16,638
Interest expense (income)	20	80	138
Net earnings (loss)	69,122	58,539	11,799
Serviacero
Investments in and Advances to Affiliates [Line Items]
Net sales	275,315	260,337	277,385
Gross margin	37,080	15,328	17,028
Operating income (loss)	29,975	11,110	14,036
Depreciation and amortization	3,862	3,508	3,462
Interest expense (income)	89	114	201
Income tax expense (benefit)	11,740	6,249	7,844
Net earnings (loss)	18,140	6,246	8,429
ArtiFlex
Investments in and Advances to Affiliates [Line Items]
Net sales	208,922	219,510	183,029
Gross margin	22,829	30,181	24,145
Operating income (loss)	15,519	22,612	16,476
Depreciation and amortization	5,850	6,105	7,258
Interest expense (income)	1,429	1,650	1,973
Income tax expense (benefit)	(2)	289	105
Net earnings (loss)	14,092	20,673	14,398
Other [Member]
Investments in and Advances to Affiliates [Line Items]
Net sales	17,784	74,214	91,144
Gross margin	(4,313)	13,142	14,201
Operating income (loss)	(8,407)	6,910	4,980
Depreciation and amortization	698	3,081	4,154
Interest expense (income)		(10)	(29)
Income tax expense (benefit)	(2)	53
Net earnings (loss)	$ (5,472)	$ 8,516	$ 4,806