Income Tax - Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	May 31, 2014	May 31, 2013	May 31, 2012
Deferred tax assets:
Share-based compensation	$ 5,916	$ 12,266
Bad debt expense	2,802	2,292
Foreign NOL carryforward	6,881	8,221
U.S. NOL carryforward	22,074	243
U.S. capital loss carryforward	1,734	20,176
Basis difference - U.K. business	96,720	90,678
Foreign tax credit	11,819	14,413
Other tax credits	1,730	1,733
Deferred tax assets, gross	149,676	150,022
Less: valuation allowance	(7,199)	(28,464)	(26,090)
Net deferred tax asset	142,477	121,558
Deferred tax liabilities:
Taxes on unremitted earnings and other	5,470	13,729
Foreign currency translation	26,813	30,163
Acquired intangibles	149,440	90,205
Prepaid expenses	1,800	2,523
Property and equipment	53,238	53,998
Deferred tax liabilities, gross	236,761	190,618
Net deferred tax liability	(94,284)	(69,060)
Less: current net deferred tax asset	12,887	6,485
Net noncurrent deferred tax liability	$ (107,171)	$ (75,545)