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Cash, Cash Equivalents and Short-Term Investments (Tables) | 9 Months Ended
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Sep. 30, 2023
Cash, Cash Equivalents and Short-Term Investments |
Schedule of cash, cash equivalents and short-term investments | Cash, cash equivalents and short-term investments consisted of the following as of September 30, 2023 and December 31, 2022 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, | ​ | December 31,
​ |  | 2023 |  | 2022
Cash | ​ | $ | 40,760 | ​ | $ | 34,752
Cash equivalents: | ​ |  | ​ | ​ | ​ | ​
Money market mutual fund | ​ |  | 18,713 | ​ | ​ | 1,843
Total cash and cash equivalents | ​ |  | 59,473 | ​ | ​ | 36,595
Short-term investments: | ​ |  | ​ | ​ | ​ | ​
U.S. Treasury notes and bills | ​ |  | 129,931 | ​ | ​ | 190,718
Mutual funds | ​ |  | 97,522 | ​ | ​ | 99,777
Corporate debt securities | ​ | ​ | 178,936 | ​ | ​ | 196,233
Total short-term investments | ​ |  | 406,389 | ​ | ​ | 486,728
Cash, cash equivalents and short-term investments | ​ | $ | 465,862 | ​ | $ | 523,323
Schedule of available-for-sale investments | The amortized cost, gross unrealized gains, gross unrealized losses and fair value of available-for-sale investments by type of security at September 30, 2023 were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​
​ |  | Cost |  | Gains |  | Losses |  | Fair Value
U.S. Treasury notes | ​ | $ | 127,887 | ​ | $ | 2,122 | ​ | $ | (78) | ​ | $ | 129,931
Corporate debt securities | ​ | ​ | 177,904 | ​ | ​ | 1,456 | ​ | ​ | (424) | ​ | ​ | 178,936
Total available-for-sale investments | ​ | $ | 305,791 | ​ | $ | 3,578 | ​ | $ | (502) | ​ | $ | 308,867
The amortized cost, gross unrealized gains, gross unrealized losses and fair value of available-for-sale investments by type of security at December 31, 2022 were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​
​ |  | Cost |  | Gains |  | Losses |  | Fair Value
U.S. Treasury notes | ​ | $ | 199,626 |  | $ | 5 | ​ | $ | (8,913) | ​ | $ | 190,718
Corporate debt securities | ​ | ​ | 210,764 |  | ​ | 1,243 |  | ​ | (15,774) | ​ | ​ | 196,233
Total available-for-sale investments | ​ | $ | 410,390 |  | $ | 1,248 | ​ | $ | (24,687) | ​ | $ | 386,951
Schedule of investments based on stated contractual maturities | The following table summarizes the fair value of available-for-sale investments based on stated contractual maturities as of September 30, 2023: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Amortized Cost |  | Fair Value
Due within one year | ​ | $ | 124,440 | ​ | $ | 126,880
Due after one year through five years | ​ | ​ | 181,351 | ​ | ​ | 181,987
Due after five years through ten years | ​ |  | — | ​ |  | —
Total | ​ | $ | 305,791 | ​ | $ | 308,867
​ The following table summarizes the fair value of available-for-sale investments based on stated contractual maturities as of December 31, 2022: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Amortized Cost |  | Fair Value
Due within one year | ​ | $ | 129,568 |  | $ | 126,776
Due after one year through five years | ​ |  | 280,822 |  |  | 260,175
Due after five years through ten years | ​ | ​ | — | ​ | ​ | —
Total | ​ | $ | 410,390 |  | $ | 386,951
Schedule of gross unrealized losses and fair value of available-for-sale debt securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position | The following table shows the Company’s gross unrealized losses and fair value of available-for-sale debt securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position at September 30, 2023:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Less than 12 Months |  | 12 Months or More |  | Total
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized
​ | ​ | Fair Value | ​ | Losses | ​ | Fair Value | ​ | Losses | ​ | Fair Value | ​ | Losses
U.S. Treasury notes | ​ | $ | 1,947 | ​ | $ | (19) | ​ | $ | 127,984 | ​ | $ | (59) | ​ | $ | 129,931 | ​ | $ | (78)
Corporate debt securities | ​ |  | 13,657 | ​ |  | (13) | ​ |  | 165,279 | ​ |  | (411) | ​ |  | 178,936 | ​ |  | (424)
Total | ​ | $ | 15,604 | ​ | $ | (32) | ​ | $ | 293,263 | ​ | $ | (470) | ​ | $ | 308,867 | ​ | $ | (502)
Schedule of unrealized losses related to equity securities held | Unrealized losses during 2023 and 2022 related to equity securities held at September 30, 2023 and 2022 are as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Nine Months Ended September 30,
​ |  | 2023 |  | 2022
Net losses recognized during the nine months on equity securities | ​ | $ | (3,765) | ​ | $ | (12,436)
Less: net gains (losses) recognized during the year on equity securities sold during the period | ​ |  | 1,510 | ​ |  | —
Unrealized losses recognized during the nine months on equity securities still held at September 30, 2023 and 2022 | ​ | $ | (2,255) | ​ | $ | (12,436)
​

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