Financial Results of Three Largest Affiliated Companies (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Investments in and Advances to Affiliates [Line Items]
Net sales	$ 1,685,743	$ 1,034,431	$ 708,779
Gross margin	330,148	238,083	189,622
Operating income	221,013	168,144	131,166
Depreciation and amortization	34,153	11,452	10,690
Interest expense	6,047	1,512	1,482
Income tax expense	15,114	10,126	5,625
Net earnings	201,733	156,679	127,837
WAVE
Investments in and Advances to Affiliates [Line Items]
Net sales	364,530	346,717	319,821
Gross margin	163,563	154,194	146,045
Operating income	127,305	116,295	111,524
Depreciation and amortization	4,142	3,991	3,767
Interest expense	3,427	1,375	1,366
Income tax expense	2,789	2,669	2,457
Net earnings	121,261	112,544	107,776
ClarkDietrich
Investments in and Advances to Affiliates [Line Items]
Net sales	564,624	165,807
Gross margin	61,703	17,115
Operating income	27,094	8,323
Depreciation and amortization	14,271	8
Interest expense	3
Net earnings	27,203	8,331
TWB
Investments in and Advances to Affiliates [Line Items]
Net sales	312,943	272,191	220,500
Gross margin	42,124	34,756	29,753
Operating income	28,141	21,470	14,982
Depreciation and amortization	3,259	3,900	3,783
Income tax expense	5,458	4,233	1,408
Net earnings	22,952	18,022	14,469
Other Affiliates
Investments in and Advances to Affiliates [Line Items]
Net sales	443,646	249,716	168,458
Gross margin	62,758	32,018	13,824
Operating income	38,473	22,056	4,660
Depreciation and amortization	12,481	3,553	3,140
Interest expense	2,617	137	116
Income tax expense	6,867	3,224	1,760
Net earnings	$ 30,317	$ 17,782	$ 5,592