Employee Benefit Plans - Schedule of net periodic costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019
Components of net periodic benefit (credit) cost:
Amortization of (gain) loss			$ (0.1)	$ 0.4
Pension Plans
Components of net periodic benefit (credit) cost:
Interest cost			0.3	0.4
Expected return on assets			(0.4)	(0.5)
Net amortization of prior service credit			0.0	0.0
Amortization of (gain) loss			0.3	0.5
Net periodic benefit (credit) cost			0.2	0.4
Pension Plans | Foreign Plan
Components of net periodic benefit (credit) cost:
Interest cost	$ 0.1	$ 0.2
Expected return on assets	(0.2)	(0.3)
Net amortization of prior service credit	0.0	0.0
Amortization of (gain) loss	0.2	0.3
Net periodic benefit (credit) cost	0.1	0.2
Post-Retirement Benefits
Components of net periodic benefit (credit) cost:
Interest cost	0.1	0.1	0.2	0.3
Expected return on assets	0.0	0.0	0.0	0.0
Net amortization of prior service credit	(0.2)	(0.1)	(0.2)	(0.1)
Amortization of (gain) loss	0.0	0.0	0.0	0.0
Net periodic benefit (credit) cost	$ (0.1)	$ 0.0	$ 0.0	$ 0.2