Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
AOCI, Net of Tax [Roll Forward]
Beginning Balance	$ 2,192,858	$ 2,201,492	$ 2,139,135
Other comprehensive (loss) income	(36,899)	(9,695)	1,460
Ending Balance	1,932,455	2,192,858	2,201,492
Foreign Currency
AOCI, Net of Tax [Roll Forward]
Beginning Balance	41,525	51,312
Other comprehensive (loss) income before reclassifications	(38,538)	(9,787)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Other comprehensive (loss) income	(38,538)	(9,787)
Ending Balance	2,987	41,525	51,312
Unrealized Loss on Derivatives
AOCI, Net of Tax [Roll Forward]
Beginning Balance	(12,615)	(14,339)
Other comprehensive (loss) income before reclassifications	37	(228)
Amounts reclassified from accumulated other comprehensive income (loss)	1,952	1,952
Other comprehensive (loss) income	1,989	1,724
Ending Balance	(10,626)	(12,615)	(14,339)
Other
AOCI, Net of Tax [Roll Forward]
Beginning Balance	(482)	1,150
Other comprehensive (loss) income before reclassifications	(350)	(1,632)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Other comprehensive (loss) income	(350)	(1,632)
Ending Balance	(832)	(482)	1,150
Other Accumulated Comprehensive Income (Loss)
AOCI, Net of Tax [Roll Forward]
Beginning Balance	28,428	38,123	36,663
Other comprehensive (loss) income before reclassifications	(38,851)	(11,647)
Amounts reclassified from accumulated other comprehensive income (loss)	1,952	1,952
Other comprehensive (loss) income	(36,899)	(9,695)
Ending Balance	$ (8,471)	$ 28,428	$ 38,123