Net Carrying Values of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Feb. 28, 2019	May 31, 2018
Available-for-Sale Securities, Amortized Cost
Less than one year, amortized cost	$ 7,646
One year through five years, amortized cost	10,718
Six years through ten years, amortized cost	4,749
After ten years, amortized cost	951
Available-for-Sale Debt Securities, Amortized Cost	24,064	$ 23,994
Available-for-Sale Securities, Fair Value
Less than one year, fair value	7,604
One year through five years, fair value	10,522
Six years through ten years, fair value	4,684
After ten years, fair value	974
Available-for-sale debt securities, fair value	$ 23,784	$ 23,516

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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