Fair Value - Additional Information (Detail) - USD ($)	Feb. 29, 2016	May. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on nonrecurring basis	$ 0	$ 12,403,000
Liabilities measured at fair value on nonrecurring basis	0
Long-term Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt at fair value including current maturities	602,511,000	610,028,000
Long-term debt at carrying amount including current maturities	$ 580,372,000	$ 580,193,000