Cash, Cash Equivalents and Short-Term Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2012
Amortized cost and Estimated Fair Value of Short-term fixed Income Securities [Abstract]
Due within one year, Amortized Cost	$ 869,849
Due between one and two years, Amortized Cost	422,844
Due between two and three years, Amortized Cost	566,140
Due after three years, Amortized Cost	210,418
Total, Amortized Cost	2,069,251
Due within one year, Estimated Fair value	871,889
Due between one and two years, Estimated Fair value	427,220
Due between two and three years, Estimated Fair value	571,649
Due after three years, Estimated Fair value	213,976
Total, Estimated Fair value	$ 2,084,734