Investments (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Short-term investments:
Total short-term investments	$ 47,507	$ 150,487
Long-term investments:
Equity Method Investments.	4,442
Total long-term investments	15,030	9,386
Investment in limited partnership fund
Long-term investments:
Equity Method Investments.	4,442
Held to maturity securities
Short-term investments:
Total short-term investments		150,487
Long-term investments:
Total long-term investments		9,386
Held to maturity securities | Municipal securities
Short-term investments:
Total short-term investments		5,332
Held to maturity securities | U.S. government securities
Short-term investments:
Total short-term investments		63,205
Long-term investments:
Total long-term investments		7,404
Held to maturity securities | Corporate bonds
Short-term investments:
Total short-term investments		81,950
Long-term investments:
Total long-term investments		$ 1,982
Available-for-sale securities
Short-term investments:
Total short-term investments	47,507
Long-term investments:
Total long-term investments	10,588
Available-for-sale securities | Municipal securities
Short-term investments:
Total short-term investments	5,244
Long-term investments:
Total long-term investments	1,592
Available-for-sale securities | U.S. government securities
Short-term investments:
Total short-term investments	33,771
Long-term investments:
Total long-term investments	8,996
Available-for-sale securities | Corporate bonds
Short-term investments:
Total short-term investments	$ 8,492