Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Retirement Benefits [Abstract]
Interest cost	$ 721	$ 781	$ 1,441	$ 1,562
Expected return on assets	(741)	(720)	(1,481)	(1,441)
Net periodic benefit cost	$ (20)	$ 61	$ (40)	$ 121