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Investments (Tables) | 12 Months Ended
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Apr. 30, 2021
Investments |
Schedule of investments | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | April 30,
​ |  | 2021 |  | 2020
Short-term investments: | ​ | ​ | ​ | ​ | ​ | ​
Available-for-sale securities: | ​ | ​ | ​ | ​ | ​ | ​
Municipal securities | ​ | ​ | 22,245 | ​ | ​ | 5,244
U.S. government securities | ​ | ​ | 4,009 | ​ | ​ | 33,771
Corporate bonds | ​ | ​ | 5,717 | ​ | ​ | 8,492
Total short-term investments | ​ | $ | 31,971 | ​ | $ | 47,507
Long-term investments: | ​ | ​ | ​ | ​ | ​ | ​
Available-for-sale securities: | ​ | ​ | ​ | ​ | ​ | ​
Municipal securities | ​ | ​ | 988 | ​ | ​ | 1,592
U.S. government securities | ​ | ​ | 4,000 | ​ | ​ | 8,996
Total available-for-sale investments | ​ |  | 4,988 | ​ |  | 10,588
Equity method investments | ​ | ​ | ​ | ​ | ​ | ​
Investment in limited partnership fund | ​ |  | 7,168 | ​ |  | 4,442
Total equity method investments | ​ |  | 7,168 | ​ |  | 4,442
Total long-term investments | ​ | $ | 12,156 | ​ | $ | 15,030
Schedule of activity related to available-for-sale investments recorded in short-term and long-term investments | The following table is a summary of the activity related to the available-for-sale investments recorded in short-term and long-term investments as of April 30, (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | April 30, 2021 | ​ | April 30, 2020 | ​
​ |  | ​ | ​ |  | Gross |  | Gross |  | ​ | ​ |  | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ |
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair | ​
​ | ​ | Cost | ​ | Gains | ​ | Losses | ​ | Value | ​ | Cost |  | Gains | ​ | Losses |  | Value | ​
Municipal securities | ​ | $ | 23,227 | ​ | $ | 8 | ​ | $ | (2) | ​ | $ | 23,233 | ​ | $ | 6,807 | ​ | $ | 29 | ​ | $ | — | ​ | $ | 6,836 | ​
U.S. government securities | ​ | ​ | 8,008 | ​ | ​ | 1 | ​ | ​ | — | ​ | ​ | 8,009 | ​ |  | 42,730 | ​ | ​ | 41 | ​ | ​ | (4) | ​ | ​ | 42,767 | ​
Corporate bonds | ​ | ​ | 5,718 | ​ | ​ | — | ​ | ​ | (1) | ​ | ​ | 5,717 | ​ |  | 8,495 | ​ | ​ | — | ​ | ​ | (3) | ​ | ​ | 8,492 | ​
Total available-for-sale investments | ​ | $ | 36,953 | ​ | $ | 9 | ​ | $ | (3) | ​ | $ | 36,959 | ​ | $ | 58,032 |  | $ | 70 | ​ | $ | (7) |  | $ | 58,095 | ​
Schedule of amortized cost, gross unrealized gains, gross unrealized losses, and estimated fair value of available-for-sale investments | The amortized cost and fair value of the Company’s available-for-sale securities by contractual maturity at April 30, 2021, are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Cost |  | Fair Value |
Due within one year | ​ | $ | 31,968 | ​ | $ | 31,971 | ​
Due after one year through five years | ​ |  | 4,985 | ​ |  | 4,988 | ​
Total | ​ | $ | 36,953 | ​ | $ | 36,959 | ​

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