Commitments and Contingencies Commitments and Contingencies (Details 1) - Revolving Credit Facility [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Line of Credit Facility [Line Items]
Maximum amount outstanding	$ 350.0	$ 150.0	$ 350.0	$ 150.0
Average Amount Borrowed	$ 225.0	$ 150.0	$ 217.0	$ 125.0
Weighted-average interest rate	3.25%	3.25%	3.25%	3.25%