Employee Benefit Plans - Obligations and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2020	May 31, 2019
Change in benefit obligation:
Projected benefit obligation, beginning of year	$ 91,935	$ 86,341
Interest cost	2,881	3,124
Actuarial loss	13,662	5,455
Benefits paid	(3,121)	(2,985)
Projected benefit obligation, end of year	105,357	91,935
Change in plan assets:
Fair value of plan assets, beginning of year	62,267	58,781
Actual return on plan assets	7,097	2,437
Employer contributions	2,098	4,034
Benefits paid	(3,121)	(2,985)
Fair value of plan assets, end of year	68,341	62,267
Funded status-net amount recognized	$ (37,016)	$ (29,668)