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Investments (Tables) | 3 Months Ended
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Oct. 31, 2020
Investments |
Schedule of investments | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | October 31, | ​ | April 30, | ​
​ |  | 2020 |  | 2020 |
Short-term investments: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Available-for-sale securities: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Municipal securities | ​ | ​ | 13,279 | ​ | ​ | 5,244 | ​
U.S. government securities | ​ | ​ | 44,024 | ​ | ​ | 33,771 | ​
Corporate bonds | ​ | ​ | 9,834 | ​ | ​ | 8,492 | ​
Total short-term investments | ​ | $ | 67,137 | ​ | $ | 47,507 | ​
Long-term investments: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Available-for-sale securities: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Municipal securities | ​ | ​ | 5,640 | ​ | ​ | 1,592 | ​
U.S. government securities | ​ | ​ | 10,001 | ​ | ​ | 8,996 | ​
Total available-for-sale investments | ​ |  | 15,641 | ​ |  | 10,588 | ​
Equity method investments | ​ | ​ | ​ | ​ | ​ | ​ | ​
Investment in limited partnership fund | ​ |  | 5,335 | ​ |  | 4,442 | ​
Total equity method investments | ​ |  | 5,335 | ​ |  | 4,442 | ​
Total long-term investments | ​ | $ | 20,976 | ​ | $ | 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 October 31, 2020 and April 30, 2020, respectively (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | October 31, 2020
​ |  | ​ | ​ |  | Gross |  | Gross |  | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
​ | ​ | Cost | ​ | Gains | ​ | Losses | ​ | Value
Municipal securities | ​ | $ | 18,915 | ​ | $ | 9 | ​ | $ | (5) | ​ | $ | 18,919
U.S. government securities | ​ | ​ | 54,022 | ​ | ​ | 3 | ​ | ​ | — | ​ | ​ | 54,025
Corporate bonds | ​ | ​ | 9,838 | ​ | ​ | — | ​ | ​ | (4) | ​ | ​ | 9,834
Total available-for-sale investments | ​ | $ | 82,775 | ​ | $ | 12 | ​ | $ | (9) | ​ | $ | 82,778
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | April 30, 2020 | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair |
​ | ​ | Cost |  | Gains | ​ | Losses |  | Value |
Municipal securities |  | $ | 6,807 | ​ | $ | 29 | ​ | $ | — | ​ | $ | 6,836 | ​
U.S. government securities | ​ |  | 42,730 | ​ | ​ | 41 | ​ | ​ | (4) | ​ | ​ | 42,767 | ​
Corporate bonds | ​ |  | 8,495 | ​ | ​ | — | ​ | ​ | (3) | ​ | ​ | 8,492 | ​
Total available-for-sale investments |  | $ | 58,032 |  | $ | 70 | ​ | $ | (7) |  | $ | 58,095 | ​
Schedule of amortized cost and fair value of the available-for-sale debt securities by contractual maturity | The amortized cost and fair value of the available-for-sale debt securities by contractual maturity at October 31, 2020 were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Cost |  | Fair Value |
Due within one year | ​ | $ | 67,135 | ​ | $ | 67,137 | ​
Due after one year through five years | ​ |  | 15,640 | ​ |  | 15,641 | ​
Total | ​ | $ | 82,775 | ​ | $ | 82,778 | ​

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- Definition Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 + Details
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- Definition Tabular disclosure of investment in equity security without readily determinable fair value. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117539-209714 + Details
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