Schedule of Progression of Liabilities Associated with Restructuring Activities, Combined with Reconciliation to Restructuring and Other Expense (Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 7,029	$ 6,229
Expense	4,589	8,713
Payments	(9,262)	(7,724)
Adjustments	185	(189)
Ending Balance	2,541	7,029	$ 6,229
Gain/loss on sale of assets	2,338	(10,589)
Less: joint venture transactions	(413)	(1,036)	604
Restructuring and other expense (income)	6,514	(2,912)	3,293
Early Retirement And Severance
Restructuring Cost and Reserve [Line Items]
Beginning Balance	6,495	5,029
Expense	3,323	6,236
Payments	(7,694)	(4,703)
Adjustments	46	(67)
Ending Balance	2,170	6,495	5,029
Facility Exit And Other Costs
Restructuring Cost and Reserve [Line Items]
Beginning Balance	534	1,200
Expense	1,266	2,477
Payments	(1,568)	(3,021)
Adjustments	139	(122)
Ending Balance	$ 371	$ 534	$ 1,200