Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	May 31, 2018	May 31, 2017
Deferred tax assets
Accounts receivable	$ 1,455	$ 2,157
Inventories	5,004	6,624
Accrued expenses	23,219	30,065
Net operating loss carry forwards	14,201	13,256
Tax credit carry forwards	811	3,206
Stock-based compensation	10,588	17,668
Other	502	205
Total deferred tax assets	55,780	73,181
Valuation allowance for deferred tax assets	(14,006)	(12,987)
Net deferred tax assets	41,774	60,194
Deferred tax liabilities
Property, plant and equipment	(74,512)	(42,599)
Investment in affiliated companies, principally due to undistributed earnings	(22,918)	(46,001)
Derivative contracts	(2,653)	(1,745)
Other	(1,879)	(4,149)
Total deferred tax liability	(101,962)	(94,494)
Net deferred tax liability	$ (60,188)	$ (34,300)