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Cash, Cash Equivalents and Short-Term Investments (Tables) | 12 Months Ended
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Dec. 31, 2022
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, 2022 and 2021 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Carrying Value
​ |  | 2022 |  | 2021
Cash | ​ | $ | 34,752 | ​ | $ | 27,788
Cash equivalents: | ​ |  | ​ | ​ | ​ | ​
Money market mutual funds | ​ |  | 1,843 | ​ | ​ | 111,313
Total cash and cash equivalents | ​ |  | 36,595 | ​ | ​ | 139,101
Short-term investments: | ​ |  | ​ | ​ | ​ | ​
U.S. Treasury notes and bills | ​ |  | 190,718 | ​ | ​ | 223,896
Mutual funds | ​ |  | 99,777 | ​ | ​ | 110,006
Corporate debt securities | ​ | ​ | 196,233 | ​ | ​ | 155,796
Total short-term investments | ​ |  | 486,728 | ​ | ​ | 489,698
Cash, cash equivalents and short-term investments | ​ | $ | 523,323 | ​ | $ | 628,799
​
Schedule of available-for-sale debt securities | 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
​ 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, 2021 were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​
​ |  | Cost |  | Gains |  | Losses |  | Fair Value
U.S. Treasury notes | ​ | $ | 226,020 | ​ | $ | 12 | ​ | ​ | (2,136) | ​ | $ | 223,896
Corporate debt securities | ​ | ​ | 157,527 | ​ | ​ | — | ​ | ​ | (1,731) | ​ | ​ | 155,796
Total available-for-sale investments | ​ | $ | 383,547 | ​ | $ | 12 | ​ | $ | (3,867) | ​ | $ | 379,692
​
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, 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
​ The following table summarizes the fair value of available-for-sale debt securities based on stated contractual maturities as of December 31, 2021 (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Amortized Cost |  | Fair Value
Due within one year | ​ | $ | 39,081 | ​ | $ | 39,035
Due after one year through five years | ​ | ​ | 328,776 | ​ | ​ | 325,047
Due after five years through ten years | ​ |  | 15,690 | ​ |  | 15,610
Total | ​ | $ | 383,547 | ​ | $ | 379,692
​
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, 2022:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 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 | ​ | $ | 19,466 | ​ | $ | (297) | ​ | $ | 171,252 | ​ | $ | (8,616) | ​ | $ | 190,718 | ​ | $ | (8,913)
Corporate debt securities | ​ |  | 61,492 | ​ |  | (2,218) | ​ |  | 134,740 | ​ |  | (13,556) | ​ |  | 196,233 | ​ |  | (15,774)
Total | ​ | $ | 80,958 | ​ | $ | (2,515) | ​ | $ | 305,992 | ​ | $ | (22,172) | ​ | $ | 386,951 | ​ | $ | (24,687)
​
Schedule of unrealized losses on investments | Unrealized gains (losses) during 2022, 2021 and 2020 related to equity securities held at December 31, 2022, 2021 and 2020 are as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2022 |  | 2021 |  | 2020
Net losses recognized during the year on equity securities | ​ | $ | (11,406) | ​ | $ | (1,386) | ​ | $ | (245)
Less: net losses recognized during the year on equity securities sold during the year | ​ |  | — | ​ |  | — | ​ | ​ | (1,090)
Unrealized gains (losses) recognized during the year on equity securities still held at December 31, 2022, 2021 and 2020 | ​ | $ | (11,406) | ​ | $ | (1,386) | ​ | $ | 845

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