Net Carrying Values of Debt Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2012
Available-for-Sale Securities, amortized cost
Less than one year, amortized cost	$ 913
One year through five years, amortized cost	29,643
Six years through ten years, amortized cost	4,557
After ten years, amortized cost	1,851
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Total	36,964
Available-for-Sale Securities, fair value
Less than one year, fair value	914
One year through five years, fair value	29,935
Six years through ten years, fair value	4,776
After ten years, fair value	2,141
Available-for-sale Securities, Debt Securities, Total	$ 37,766