Retirement and Death Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	May 31, 2016	May 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee retirement or disability, period over which benefits are to be paid	10 years
Life insurance contracts, discounting rate for present value calculation	4.00%	4.00%
Life insurance contracts, current and non current amounts recognized in balance Sheet	$ 5,340,000	$ 5,707,000
Life insurance contracts, amount charged to operations	$ 10,000	$ 161,000