Derivatives & Risk Management - Summary of Location of Gains and Losses on the Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Realized (gain) loss on derivatives	$ (746)	$ (1,431)	$ (1,983)	$ (4,878)
Foreign currency forward contracts \| Realized gain on derivatives \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Realized (gain) loss on derivatives	(746)	(1,431)	(1,983)	(4,878)
Foreign currency forward contracts \| Unrealized loss on derivatives \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Realized (gain) loss on derivatives	2,589	56	1,224	994
Variable cash settlement \| Selling, general and administrative expenses \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Realized (gain) loss on derivatives	$ 279	$ (43)	$ 453	$ (279)