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Cash, Cash Equivalents and Short-Term Investments (Tables) | 3 Months Ended
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Mar. 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 March 31, 2023 and December 31, 2022 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, | ​ | December 31,
​ |  | 2023 |  | 2022
Cash | ​ | $ | 36,000 | ​ | $ | 34,752
Cash equivalents: | ​ |  | ​ | ​ | ​ | ​
Money market mutual fund | ​ |  | 2,538 | ​ | ​ | 1,843
Total cash and cash equivalents | ​ |  | 38,538 | ​ | ​ | 36,595
Short-term investments: | ​ |  | ​ | ​ | ​ | ​
U.S. Treasury notes and bills | ​ |  | 190,833 | ​ | ​ | 190,718
Mutual funds | ​ |  | 101,287 | ​ | ​ | 99,777
Corporate debt securities | ​ | ​ | 191,956 | ​ | ​ | 196,233
Total short-term investments | ​ |  | 484,076 | ​ | ​ | 486,728
Cash, cash equivalents and short-term investments | ​ | $ | 522,614 | ​ | $ | 523,323
​
Schedule of available-for-sale debt investments | The amortized cost, gross unrealized gains, gross unrealized losses and fair value of available-for-sale investments by type of security at March 31, 2023 were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​
​ |  | Cost |  | Gains |  | Losses |  | Fair Value
U.S. Treasury notes | ​ | $ | 188,726 | ​ | $ | 2,108 | ​ | $ | (1) | ​ | $ | 190,833
Corporate debt securities | ​ | ​ | 190,389 | ​ | ​ | 1,790 | ​ | ​ | (223) | ​ | ​ | 191,956
Total available-for-sale investments | ​ | $ | 379,115 | ​ | $ | 3,898 | ​ | $ | (224) | ​ | $ | 382,789
​ 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 March 31, 2023: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Amortized Cost |  | Fair Value
Due within one year | ​ | $ | 142,192 | ​ | $ | 143,467
Due after one year through five years | ​ |  | 236,923 | ​ | ​ | 239,322
Due after five years through ten years | ​ | ​ | — | ​ | ​ | —
Total | ​ | $ | 379,115 | ​ | $ | 382,789
​ 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 March 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 |  | $ | 14,573 |  | $ | (1) |  | $ | 176,260 |  | $ | — |  | $ | 190,833 |  | $ | (1)
Corporate debt securities | ​ |  | 41,521 | ​ |  | (11) | ​ |  | 150,435 | ​ |  | (212) | ​ |  | 191,956 | ​ |  | (223)
Total | ​ | $ | 56,094 | ​ | $ | (12) | ​ | $ | 326,695 | ​ | $ | (212) | ​ | $ | 382,789 | ​ | $ | (224)
​
Schedule of unrealized losses on investments | Unrealized losses during 2023 and 2022 related to equity securities held at March 31, 2023 and 2022 are as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended March 31,
​ |  | 2023 |  | 2022
Net losses recognized during the three months on equity securities | ​ | $ | — | ​ | $ | (4,908)
Less: net gains (losses) recognized during the year on equity securities sold during the period | ​ |  | 1,510 | ​ | ​ | —
Unrealized losses recognized during the three months on equity securities still held at March 31, 2023 and 2022 | ​ | $ | 1,510 | ​ | $ | (4,908)

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