Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	Feb. 29, 2020	Feb. 28, 2019
Accumulated Other Comprehensive Loss
Balance at beginning of the period	$ (40.0)		$ (40.9)	$ (32.6)		$ (32.0)	$ (40.9)	$ (32.0)
Other comprehensive income (loss) before reclassifications	(0.1)			0.5			0.3	(0.6)
Amounts reclassified from AOCL	0.2			0.3			0.7	0.8
Other comprehensive income, net of tax	0.1	$ 0.8	0.1	0.8	$ (0.4)	(0.2)	1.0	0.2
Balance at end of the period	(39.9)	(40.0)		(31.8)	(32.6)		(39.9)	(31.8)
Currency Translation Adjustments
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(1.7)		(2.1)	(0.8)		0.3	(2.1)	0.3
Other comprehensive income (loss) before reclassifications	(0.1)			0.5			0.3	(0.6)
Other comprehensive income, net of tax	(0.1)			0.5			0.3	(0.6)
Balance at end of the period	(1.8)	(1.7)		(0.3)	(0.8)		(1.8)	(0.3)
Pensions Plans
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(38.3)		$ (38.8)	(31.8)		$ (32.3)	(38.8)	(32.3)
Amounts reclassified from AOCL	0.2			0.3			0.7	0.8
Other comprehensive income, net of tax	0.2			0.3			0.7	0.8
Balance at end of the period	$ (38.1)	$ (38.3)		$ (31.5)	$ (31.8)		$ (38.1)	$ (31.5)