Leases - Supplemental cash flow information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Nov. 30, 2019 USD ($)	Nov. 30, 2019 USD ($)
Leases
Weighted-average remaining lease term (years)	8 years 10 months 24 days	8 years 10 months 24 days
Weighted-average discount rate	3.40%	3.40%
Cash paid for amounts included in the measurement of lease liabilities	$ 3.9	$ 7.6
Operating lease liabilities arising from obtaining ROU assets	$ 13.1	$ 13.1