Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016	Feb. 28, 2017
Operating Leased Assets [Line Items]
Operating lease expense	$ 26.0	$ 24.9	$ 25.7
Capital lease amortization expense	1.3	1.1	$ 0.8
Open standby letters of credit	$ 5.3	$ 5.3
Minimum [Member]
Operating Leased Assets [Line Items]
Capital lease period	1 year
Maximum [Member]
Operating Leased Assets [Line Items]
Capital lease period	10 years
State Sales Tax Assessment [Member] | Wisconsin [Member]
Operating Leased Assets [Line Items]
Sales and Excise Tax Payable				$ 5.4