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Cash, Cash Equivalents and Short-Term Investments (Tables) | 12 Months Ended
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Dec. 31, 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 December 31, 2023 and 2022 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, | ​ | Carrying Value
​ |  | 2023 |  | 2022 |  | 2023 |  | 2022
Cash | ​ | $ | 40,979 | ​ | $ | 34,752 | ​ | $ | 40,979 | ​ | $ | 34,752
Cash equivalents: | ​ |  | ​ | ​ | ​ | ​ | ​ |  | ​ | ​ | ​ | ​
Money market mutual fund | ​ |  | 5,367 | ​ | ​ | 1,843 | ​ |  | 5,367 | ​ | ​ | 1,843
Total cash and cash equivalents | ​ |  | 46,346 | ​ | ​ | 36,595 | ​ |  | 46,346 | ​ | ​ | 36,595
Short-term investments: | ​ |  | ​ | ​ | ​ | ​ | ​ |  | ​ | ​ | ​ | ​
U.S. Treasury notes | ​ |  | 136,665 | ​ | ​ | 190,718 | ​ |  | 136,665 | ​ | ​ | 190,718
Mutual funds | ​ |  | 101,085 | ​ | ​ | 99,777 | ​ |  | 101,085 | ​ | ​ | 99,777
Corporate debt securities | ​ | ​ | 172,658 | ​ | ​ | 196,233 | ​ | ​ | 172,658 | ​ | ​ | 196,233
Total short-term investments | ​ |  | 410,409 | ​ | ​ | 486,728 | ​ |  | 410,409 | ​ | ​ | 486,728
Cash, cash equivalents and short-term investments | ​ | $ | 456,755 | ​ | $ | 523,323 | ​ | $ | 456,755 | ​ | $ | 523,323
​
Schedule of available-for-sale investments | The amortized cost, gross unrealized gains, gross unrealized losses and fair value of available-for-sale debt securities by type of security at December 31, 2023 were as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​
​ |  | Cost |  | Gains |  | Losses |  | Fair Value
U.S. Treasury notes | ​ | $ | 133,989 | ​ | $ | 2,697 | ​ | $ | (21) | ​ | $ | 136,665
Corporate debt securities | ​ | ​ | 168,592 | ​ | ​ | 4,067 | ​ | ​ | (1) | ​ | ​ | 172,658
Total available-for-sale investments | ​ | $ | 302,581 | ​ | $ | 6,764 | ​ | $ | (22) | ​ | $ | 309,323
​ The amortized cost, gross unrealized gains, gross unrealized losses and fair value of available-for-sale debt securities 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 debt securities based on stated contractual maturities as of December 31, 2023:
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Amortized Cost |  | Fair Value
Due within one year | ​ | $ | 101,252 | ​ | $ | 103,802
Due after one year through five years | ​ | ​ | 201,329 | ​ | ​ | 205,521
Total | ​ | $ | 302,581 | ​ | $ | 309,323
The following table summarizes the fair value of available-for-sale debt securities based on stated contractual maturities as of December 31, 2022 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 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 December 31, 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 | ​ | $ | 44,693 | ​ | $ | (21) | ​ | $ | 91,972 | ​ | $ | — | ​ | $ | 136,665 | ​ | $ | (21)
Corporate debt securities | ​ |  | 9,033 | ​ |  | (1) | ​ |  | 163,625 | ​ |  | — | ​ |  | 172,658 | ​ |  | (1)
Total | ​ | $ | 53,726 | ​ | $ | (22) | ​ | $ | 255,597 | ​ | $ | — | ​ | $ | 309,323 | ​ | $ | (22)
Schedule of unrealized gains (losses) related to equity securities held | Unrealized gains (losses) during 2023, 2022 and 2021 related to equity securities held at December 31, 2023, 2022 and 2021 are as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Year Ended December 31,
​ |  | 2023 |  | 2022 |  |  | 2021
Net losses recognized during the twelve months on equity securities | ​ | $ | (3,764) | ​ | $ | (11,406) | ​ | $ | (1,386)
Less: net gains recognized during the year on equity securities sold during the year | ​ |  | 5,072 | ​ |  | — | ​ |  | —
Unrealized gains (losses) recognized during the year on equity securities still held at December 31, 2023, 2022 and 2021 | ​ | $ | 1,308 | ​ | $ | (11,406) | ​ | $ | (1,386)
​

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