Employee Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	$ 27,600,000	$ 28,000,000
Unrecognized net actuarial loss	$ 800,000	$ 1,200,000
Expected return on plan assets (as a percent)	4.90%	5.40%
Expected contributions next twelve months	$ 4,300,000
Expected contributions in year two	3,200,000
Expected contributions in year three	3,400,000
Expected contributions in year four	3,600,000
Expected contributions in year five	3,700,000
Expected contributions in year six	3,900,000
Expected contributions thereafter	21,400,000
Fair value of plan assets	58,781,000	$ 59,396,000	$ 0
Projected benefit obligation	86,341,000	87,387,000	0
Estimated contribution to pension plan	0
Net periodic benefit expense (income)	(14,000)	(28,000)
Supplemental Executive Retirement Plan (SERP)
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 8,200,000	6,900,000	6,600,000
United States Plan
Defined Benefit Plan Disclosure [Line Items]
Required years of service for plan eligibility (years)	1 year
Employer contributions	$ 56,700,000	47,500,000	43,100,000
Deferred Profit Sharing Plan (DPSP)
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	2,800,000	1,800,000	$ 1,600,000
Pension Plan of Immaterial Acquisitions
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,500,000	7,100,000
Projected benefit obligation	7,400,000	7,500,000
Net periodic benefit expense (income)	$ (100,000)	$ 100,000