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, 2020	May 31, 2019
Investments Debt And Equity Securities [Abstract]
Total investments with unrealized losses, fair value	$ 2,028	$ 11,508
Unrealized losses with a loss position for less than 12 months, fair value		806
Unrealized losses with a loss position for more than 12 months, fair value	2,028	10,702
Total investments with unrealized losses, gross unrealized losses	(40)	(311)
Unrealized losses with a loss position for less than 12 months, gross unrealized losses		(2)
Unrealized losses with a loss position for more than 12 months, gross unrealized losses	$ (40)	$ (309)