Net Carrying Values of Debt Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2013	May 31, 2013
Available-for-Sale Securities, amortized cost
Less than one year, amortized cost	$ 3,210
One year through five years, amortized cost	12,055
Six years through ten years, amortized cost	4,712
After ten years, amortized cost	1,451
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Total	21,428
Available-for-Sale Securities, fair value
Less than one year, fair value	3,227
One year through five years, fair value	12,118
Six years through ten years, fair value	4,647
After ten years, fair value	1,569
Marketable debt securities, carrying value	$ 21,561	$ 22,801