Savings Plan, Employee Stock Ownership Plan and Retirement Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Postemployment Benefits Disclosure [Line Items]
Contributions to Retirement Plan	$ 848	$ 784	$ 749
Other assets	13,743	22,150
Supplemental Executive Retirement Plan [SERP]
Postemployment Benefits Disclosure [Line Items]
Contributions to Retirement Plan	22	25	$ 29
Accrued Expense	3,521	3,418
Other assets	$ 3,521	$ 3,418
ESOP
Postemployment Benefits Disclosure [Line Items]
ESOP termination date	2013