Employee Pension Plans - Summary of Defined Benefit Plan's Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	May 31, 2018	May 31, 2017	May 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	$ 27,212	$ 27,022	$ 25,566
Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	27,212	27,022
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	291	294
Money Market Funds | Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	291	294
Bond Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	14,887	14,613
Bond Funds | Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	14,887	14,613
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	12,034	12,115
Equity Funds | Quoted Prices In Active Markets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit plan assets fair value	$ 12,034	$ 12,115