Net Carrying Values of Debt Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2014	May 31, 2014
Available-for-Sale Securities, amortized cost
Less than one year, amortized cost	$ 2,995
One year through five years, amortized cost	14,715
Six years through ten years, amortized cost	3,261
After ten years, amortized cost	1,119
Available-for-sale Debt Securities, Amortized Cost Basis, Total	22,090
Available-for-Sale Securities, fair value
Less than one year, fair value	2,998
One year through five years, fair value	14,638
Six years through ten years, fair value	3,292
After ten years, fair value	1,330
Marketable debt securities, carrying value	$ 22,258	$ 23,080