Deferred Tax Assets and Liabilities (Detail) - USD ($)	May. 31, 2015	May. 31, 2014
Deferred tax assets
Accounts receivable	$ 1,895,000	$ 2,400,000
Inventories	8,051,000	7,210,000
Accrued expenses	33,678,000	40,873,000
Net operating and capital loss carry forwards	14,326,000	19,302,000
Tax credit carry forwards	3,688,000	203,000
Stock-based compensation	20,434,000	12,573,000
Derivative contracts	9,177,000	1,838,000
Other	247,000	541,000
Total deferred tax assets	91,496,000	84,940,000
Valuation allowance for deferred tax assets	(13,036,000)	(21,701,000)
Net deferred tax assets	78,460,000	63,239,000
Deferred tax liabilities
Property, plant and equipment	(39,433,000)	(67,472,000)
Undistributed earnings of unconsolidated affiliates	(35,165,000)	(39,429,000)
Other	(2,150,000)	(3,395,000)
Total deferred tax liabilities	(76,748,000)	(110,296,000)
Net deferred tax asset (liability)	$ 1,712,000	$ (47,057,000)