Employee Benefit Plans - Obligations and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2019	May 31, 2018
Change in benefit obligation:
Projected benefit obligation, beginning of year	$ 86,341	$ 87,387
Interest cost	3,124	2,818
Actuarial loss (gain)	5,455	(940)
Benefits paid	(2,985)	(2,924)
Projected benefit obligation, end of year	91,935	86,341
Change in plan assets:
Fair value of plan assets, beginning of year	58,781	59,396
Actual return on plan assets	2,437	2,309
Employer contributions	4,034	0
Benefits paid	(2,985)	(2,924)
Fair value of plan assets, end of year	62,267	58,781
Funded status-net amount recognized	$ (29,668)	$ (27,560)