Fair Value Measurements (Financial Instruments on a Recurring Basis) (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Aug. 31, 2014	May 31, 2014
Level 1
Fair value on a recurring basis
Cash and cash equivalents	$ 581,453	$ 513,288
Total assets at fair value	581,453	513,288
Current accrued liabilities	0	0
Total liabilities at fair value	0	0
Level 2
Fair value on a recurring basis
Cash and cash equivalents	0	0
Total assets at fair value	0	0
Total liabilities at fair value	265	286
Level 3
Fair value on a recurring basis
Cash and cash equivalents	0	0
Total assets at fair value	0	0
Current accrued liabilities	0	0
Total liabilities at fair value	0	0
Fair Value
Fair value on a recurring basis
Cash and cash equivalents	581,453	513,288
Total assets at fair value	581,453	513,288
Current accrued liabilities	265	286
Total liabilities at fair value	265	286
Foreign Exchange Forward | Level 2
Fair value on a recurring basis
Current accrued liabilities	$ 265	$ 286