Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Feb. 28, 2022	Nov. 30, 2021	Aug. 31, 2021	Feb. 28, 2021	Nov. 30, 2020	Aug. 31, 2020	Feb. 28, 2022	Feb. 28, 2021
Accumulated Other Comprehensive Loss
Balance at beginning of the period	$ (22.2)		$ (18.3)	$ (43.0)		$ (44.6)	$ (18.3)	$ (44.6)
Other comprehensive income (loss) before reclassifications	1.7			0.4			(2.8)	1.5
Amounts reclassified from AOCL	0.4			0.2			1.0	0.7
Total other comprehensive income (loss)	2.1	$ (3.6)	(0.3)	0.6	$ 0.1	1.5	(1.8)	2.2
Balance at end of the period	(20.1)	(22.2)		(42.4)	(43.0)		(20.1)	(42.4)
Currency Translation Adjustments
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(0.6)		3.9	0.3		(2.0)	3.9	(2.0)
Other comprehensive income (loss) before reclassifications	(0.5)			0.2			(5.0)	2.5
Total other comprehensive income (loss)	(0.5)			0.2			(5.0)	2.5
Balance at end of the period	(1.1)	(0.6)		0.5	0.3		(1.1)	0.5
Pensions Plans
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(21.6)		$ (22.2)	(43.3)		$ (42.6)	(22.2)	(42.6)
Other comprehensive income (loss) before reclassifications	2.2			0.2			2.2	(1.0)
Amounts reclassified from AOCL	0.4			0.2			1.0	0.7
Total other comprehensive income (loss)	2.6			0.4			3.2	(0.3)
Balance at end of the period	$ (19.0)	$ (21.6)		$ (42.9)	$ (43.3)		$ (19.0)	$ (42.9)