Treasury Stock - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	28 Months Ended
	Nov. 30, 2017	Nov. 30, 2017	Nov. 30, 2017	Jul. 22, 2015
Stockholders' Equity Attributable to Parent [Abstract]
Increase in authorized amount of stock to be repurchased				$ 50.0
Treasury stock acquired	$ 8.6	$ 13.3	$ 24.7