Summary of Defined Benefit Plan's Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2014	May 31, 2013	May 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	$ 26,470	$ 24,442	$ 19,746
Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	26,470	24,442
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	1,099	939
Money Market Funds | Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	1,099	939
Bond Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	11,570	6,274
Bond Funds | Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	11,570	6,274
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	13,801	17,229
Equity Funds | Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	$ 13,801	$ 17,229