Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Accumulated Other Comprehensive Loss
Balance at beginning of the period	$ (39.9)	$ (44.4)
Other comprehensive income (loss) before reclassifications from AOCL	0.6	(1.5)
Amounts reclassified from AOCL	0.3	0.3
Other comprehensive income (loss), net of tax	0.9	(1.2)
Balance at end of the period	(39.0)	(45.6)
Currency Translation Adjustments
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(1.7)	(1.1)
Other comprehensive income (loss) before reclassifications from AOCL	0.6	(1.5)
Other comprehensive income (loss), net of tax	0.6	(1.5)
Balance at end of the period	(1.1)	(2.6)
Pensions Plans
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(38.2)	(43.3)
Amounts reclassified from AOCL	0.3	0.3
Other comprehensive income (loss), net of tax	0.3	0.3
Balance at end of the period	$ (37.9)	$ (43.0)