Net Carrying Values of Debt Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2014	May 31, 2013
Available-for-Sale Securities, amortized cost
Less than one year, amortized cost	$ 2,560
One year through five years, amortized cost	11,690
Six years through ten years, amortized cost	4,568
After ten years, amortized cost	1,413
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Total	20,231
Available-for-Sale Securities, fair value
Less than one year, fair value	2,553
One year through five years, fair value	11,720
Six years through ten years, fair value	4,483
After ten years, fair value	1,558
Marketable debt securities, carrying value	$ 20,314	$ 22,801