Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019
Retirement Benefits [Abstract]
Interest cost	$ 513	$ 721	$ 1,025	$ 1,441
Expected return on assets	(731)	(741)	(1,462)	(1,481)
Amortization of net loss	55	0	111	0
Net periodic pension benefit	$ (163)	$ (20)	$ (326)	$ (40)