Employee Benefit Plans - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	$ 37,000	$ 29,700
Unrecognized net actuarial loss	$ 16,200	$ 6,700
Expected return on plan assets	4.80%	4.90%
Expected contributions next twelve months	$ 4,400
Expected contributions in year two	3,900
Expected contributions in year three	4,100
Expected contributions in year four	4,200
Expected contributions in year five	4,400
Expected contributions in year six	4,500
Expected contributions thereafter	24,300
Fair value of plan assets	68,341	$ 62,267	$ 58,781
Projected benefit obligation	105,357	91,935	86,341
Net periodic pension (benefit) cost	(80)	242
Employer contributions	2,098	4,034
Supplemental Executive Retirement Plan (SERP)
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 8,400	8,600	8,200
United States Plan
Defined Benefit Plan Disclosure [Line Items]
Required years of service for plan eligibility	1 year
Employer contributions	$ 74,300	67,600	56,700
Canada | DPSP and RRSP
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	2,600	2,500	$ 2,800
Pension Plan of Immaterial Acquisitions
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,300	7,300
Projected benefit obligation	$ 9,400	$ 7,900