Financial Results of Three Largest Affiliated Companies (Detail) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Investments in and Advances to Affiliates [Line Items]
Net sales	$ 1,510,180	$ 1,492,802	$ 1,753,734
Gross margin	302,006	312,620	332,849
Operating income	193,531	213,932	230,924
Depreciation and amortization	35,662	36,958	40,712
Interest expense	8,695	9,222	8,894
Income tax expense	10,488	9,854	6,856
Net earnings	178,102	196,131	216,002
WAVE
Investments in and Advances to Affiliates [Line Items]
Net sales	382,451	382,821	370,702
Gross margin	181,102	177,935	167,924
Operating income	147,603	144,167	137,202
Depreciation and amortization	4,150	4,916	3,919
Interest expense	6,412	6,464	6,280
Income tax expense	2,539	3,606	2,451
Net earnings	138,670	134,019	128,614
ClarkDietrich
Investments in and Advances to Affiliates [Line Items]
Net sales	576,171	549,267	547,971
Gross margin	65,530	73,803	75,580
Operating income	10,436	27,918	35,024
Depreciation and amortization	16,638	16,253	18,173
Interest expense	138	103	3
Net earnings	11,799	27,837	35,005
TWB
Investments in and Advances to Affiliates [Line Items]
Net sales		54,003	344,065
Gross margin		6,109	41,116
Operating income		4,273	28,241
Depreciation and amortization		880	5,123
Income tax expense		478	1,218
Net earnings		4,023	27,931
Other Affiliates
Investments in and Advances to Affiliates [Line Items]
Net sales	551,558	506,711	490,996
Gross margin	55,374	54,773	48,229
Operating income	35,492	37,574	30,457
Depreciation and amortization	14,874	14,909	13,497
Interest expense	2,145	2,655	2,611
Income tax expense	7,949	5,770	3,187
Net earnings	$ 27,633	$ 30,252	$ 24,452