Derivatives & Risk Management - Summary of Location of Gains and Losses on the Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain on derivatives	$ (1,378)	$ (1,271)	$ (1,237)	$ (3,447)
Foreign currency forward contracts \| Realized gain on derivatives \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain on derivatives	(1,378)	(1,271)	(1,237)	(3,447)
Foreign currency forward contracts \| Unrealized (gain) loss on derivatives \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain on derivatives	682	(563)	(1,365)	939
Variable cash settlement \| Selling, general and administrative expenses \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain on derivatives	$ 63	$ (68)	$ 175	$ (237)