Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2019	May 31, 2018
Retirement Benefits [Abstract]
Interest cost	$ 3,124	$ 2,818
Expected return on assets	(2,882)	(2,832)
Net periodic benefit cost	$ 242	$ (14)