Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2018	May 31, 2017
Retirement Benefits [Abstract]
Interest cost	$ 2,818	$ 562
Expected return on assets	(2,832)	(590)
Amortization of net loss	0	0
Net periodic benefit cost	$ (14)	$ (28)