Cash, Cash Equivalents and Short-Term Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2014
Amortized cost and Estimated Fair Value of Short-term fixed Income Securities [Abstract]
Due within one year, Amortized Cost	$ 595,088
Due between one and two years, Amortized Cost	881,962
Due between two and three years, Amortized Cost	697,464
Due after three years, Amortized Cost	213,213
Total, Amortized Cost	2,387,727
Due within one year, Estimated Fair value	596,510
Due between one and two years, Estimated Fair value	885,816
Due between two and three years, Estimated Fair value	701,525
Due after three years, Estimated Fair value	213,869
Total, Estimated Fair value	$ 2,397,720