Cash, Cash Equivalents and Investments (Fair Value of Debt Securities by Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified					3 Months Ended
	Aug. 31, 2013		Nov. 30, 2012		Aug. 31, 2013 Minimum [Member]	Aug. 31, 2013 Maximum [Member]
Cash, Cash Equivalents and Investments [Line Items]
Due in one year or less	$ 39,011	[1]	$ 55,001	[1]
Due after one year	14,202		24,745
Total	$ 53,213		$ 79,746
Remaining contractual maturity of investments (in years)					11 years	30 years

[1] Includes ARS which are tendered for interest-rate setting purposes periodically throughout the year. Beginning in February 2008, auctions for these securities began to fail, and therefore these investments currently lack short-term liquidity. The remaining contractual maturities of these securities range from 11 to 30 years.