Summary of Available-for-Sale Debt Securities by Asset Type (Detail) - USD ($) $ in Thousands	May 31, 2021	May 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-Sale Debt Securities, Amortized Cost	$ 26,297	$ 25,605
Available-for-Sale Debt Securities, Gross Unrealized Gains	632	1,357
Available-for-Sale Debt Securities, Gross Unrealized Losses	(184)	(40)
Available-for-Sale Debt Securities, Fair Value (Net Carrying Amount)	26,745	26,922
U.S. Treasury and other government
Debt Securities, Available-for-sale [Line Items]
Available-for-Sale Debt Securities, Amortized Cost	26,154	25,462
Available-for-Sale Debt Securities, Gross Unrealized Gains	593	1,314
Available-for-Sale Debt Securities, Gross Unrealized Losses	(184)	(40)
Available-for-Sale Debt Securities, Fair Value (Net Carrying Amount)	26,563	26,736
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-Sale Debt Securities, Amortized Cost	143	143
Available-for-Sale Debt Securities, Gross Unrealized Gains	39	43
Available-for-Sale Debt Securities, Fair Value (Net Carrying Amount)	$ 182	$ 186

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount 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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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