Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2016	Nov. 30, 2015	Nov. 30, 2016	Nov. 30, 2015
Accumulated Other Comprehensive Loss
Balance at beginning of the period	$ (45.6)	$ (40.0)	$ (44.4)	$ (40.4)
Other comprehensive income (loss) before reclassifications from AOCL	(1.1)	0.8	(2.6)	1.0
Amounts reclassified from AOCL	0.2	0.3	0.5	0.5
Other comprehensive income (loss), net of tax	(0.9)	1.1	(2.1)	1.5
Balance at end of the period	(46.5)	(38.9)	(46.5)	(38.9)
Currency Translation Adjustments
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(2.6)	(0.9)	(1.1)	0.9
Reclassification within AOCL				(2.0)
Other comprehensive income (loss) before reclassifications from AOCL	(1.1)	0.8	(2.6)	1.0
Other comprehensive income (loss), net of tax	(1.1)	0.8	(2.6)	1.0
Balance at end of the period	(3.7)	(0.1)	(3.7)	(0.1)
Pensions Plans
Accumulated Other Comprehensive Loss
Balance at beginning of the period	(43.0)	(39.1)	(43.3)	(41.3)
Reclassification within AOCL				2.0
Amounts reclassified from AOCL	0.2	0.3	0.5	0.5
Other comprehensive income (loss), net of tax	0.2	0.3	0.5	0.5
Balance at end of the period	$ (42.8)	$ (38.8)	$ (42.8)	$ (38.8)