Investments (Details) - USD ($) $ in Thousands	Apr. 30, 2022	Apr. 30, 2021
Short-term investments:
Total short-term investments	$ 24,716	$ 31,971
Long-term investments:
Equity Method Investments.	15,433	7,168
Total long-term investments	15,433	12,156
Investment in limited partnership fund
Long-term investments:
Equity Method Investments.	15,433	7,168
Available-for-sale securities.
Short-term investments:
Total short-term investments	24,716	31,971
Long-term investments:
Total long-term investments		4,988
Available-for-sale securities. | Municipal securities
Short-term investments:
Total short-term investments	19,725	22,245
Long-term investments:
Total long-term investments		988
Available-for-sale securities. | U.S. government securities
Short-term investments:
Total short-term investments	$ 4,991	4,009
Long-term investments:
Total long-term investments		4,000
Available-for-sale securities. | Corporate bonds
Short-term investments:
Total short-term investments		$ 5,717