Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Related Party Transaction [Line Items]
Net sales to affiliates	$ 32,277,000	$ 31,441,000	$ 19,568,000
Purchases from affiliates	8,021,000	9,387,000	$ 4,930,000
Receivables from affiliates	5,826,000	4,124,000
Payable to affiliates	$ 11,528,000	$ 12,716,000