Employee Pension Plans - Components of Net Periodic Pension Cost for the Defined Benefit Plan and Defined Contribution Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016
Compensation And Retirement Disclosure [Abstract]
Interest cost	$ 1,522	$ 1,527	$ 1,621
Actuarial (return) loss on plan assets	(1,361)	(2,224)	1,154
Net amortization and deferral	(20)	1,025	(2,664)
Net periodic pension cost on defined benefit plan	141	328	111
Defined contribution plans	14,972	14,542	13,300
Total retirement plan cost	$ 15,113	$ 14,870	$ 13,411