Summary of Available-for-Sale Debt Securities in Unrealized Loss Position and Included in Accumulated Other Comprehensive (Loss), Aggregated by Length of Time Investments (Detail) - USD ($) $ in Thousands	May 31, 2021	May 31, 2020
Investments Debt And Equity Securities [Abstract]
Total investments with unrealized losses, fair value	$ 8,420	$ 2,028
Unrealized losses with a loss position for less than 12 months, fair value	6,920
Unrealized losses with a loss position for more than 12 months, fair value	1,500	2,028
Total investments with unrealized losses, gross unrealized losses	(184)	(40)
Unrealized losses with a loss position for less than 12 months, gross unrealized losses	(152)
Unrealized losses with a loss position for more than 12 months, gross unrealized losses	$ (32)	$ (40)