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Marketable Securities | 3 Months Ended
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Mar. 31, 2021
Marketable Securities |
Marketable Securities | 5. Marketable and Equity Securities ​ The Company’s marketable debt securities held as of March 31, 2021 and December 31, 2020 are summarized below: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ |  | Amortized |  | Unrealized | ​ | Unrealized |  | ​
March 31, 2021 | ​ | Cost | ​ | Gains | ​ | Losses | ​ | Fair Value
(in thousands) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Money Market Funds | ​ | $ | 165,350 | ​ | $ | — | ​ | $ | — | ​ | $ | 165,350
Corporate Securities | ​ | ​ | 73,922 | ​ | ​ | 12 | ​ | ​ | (5) | ​ | ​ | 73,929
Government Securities | ​ | ​ | 319,931 | ​ | ​ | 107 | ​ | ​ | (7) | ​ | ​ | 320,031
​ | ​ | $ | 559,203 | ​ | $ | 119 | ​ | $ | (12) | ​ | $ | 559,310
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Reported as | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Cash and cash equivalents | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 165,350
Marketable securities | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | 393,960
Total investments | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 559,310
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ |  | Amortized |  | Unrealized | ​ | Unrealized |  | ​
December 31, 2020 | ​ | Cost | ​ | Gains | ​ | Losses | ​ | Fair Value
(in thousands) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Money Market Funds | ​ | $ | 158,937 | ​ | $ | — | ​ | $ | — | ​ | $ | 158,937
Corporate Securities | ​ | ​ | 119,782 | ​ | ​ | 57 | ​ | ​ | (6) | ​ | ​ | 119,833
Government Securities | ​ | ​ | 315,319 | ​ | ​ | 37 | ​ | ​ | (3) | ​ | ​ | 315,353
​ | ​ | $ | 594,038 | ​ | $ | 94 | ​ | $ | (9) | ​ | $ | 594,123
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Reported as | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Cash and cash equivalents | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 158,937
Marketable securities | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | 435,186
Total investments | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 594,123
​ The maturities of the Company’s marketable debt securities are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized |  | Estimated
March 31, 2021 | ​ | Cost | ​ | Fair Value
(in thousands) | ​ | ​ | ​ | ​ | ​ | ​
Mature in one year or less | ​ | $ | 368,762 | ​ | $ | 368,878
Mature within two years | ​ | ​ | 25,091 | ​ | ​ | 25,082
​ | ​ | $ | 393,853 | ​ | $ | 393,960
​ ​ The unrealized losses on available-for-sale investments and their related fair values as of March 31, 2021 and December 31, 2020 are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 months | ​ | 12 months or greater
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized
March 31, 2021 | ​ | Fair value | ​ | losses | ​ | Fair value | ​ | losses
(in thousands) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Corporate Securities | ​ | $ | 4,102 | ​ | $ | (2) | ​ | $ | 3,066 | ​ | $ | (3)
Government Securities | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 14,990 | ​ | ​ | (7)
​ | ​ | $ | 4,102 | ​ | $ | (2) | ​ | $ | 18,056 | ​ | $ | (10)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 months | ​ | 12 months or greater
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​ | ​ | Unrealized
December 31, 2020 | ​ | Fair value | ​ | losses | ​ | Fair value | ​ | losses
(in thousands) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Corporate Securities | ​ | $ | 15,843 | ​ | $ | (6) | ​ | $ | — | ​ | $ | —
Government Securities | ​ | ​ | 40,802 | ​ | ​ | (3) | ​ | ​ | — | ​ | ​ | —
​ | ​ | $ | 56,645 | ​ | $ | (9) | ​ | $ | — | ​ | $ | —
​ The unrealized losses from the listed securities are primarily due to a change in the interest rate environment and not a change in the credit quality of the securities. ​ In 2020, the Company received shares of common stock of Aimmune Therapeutics, Inc. (Aimmune) and shares of common stock of Viridian Therapeutics, Inc. (Viridian, formerly MiRagen Therapeutics, Inc.) in connection with the Aimmune and Viridian licensing arrangements (both as defined below). The Aimmune common stock was redeemed for cash within the same year; the Viridian common stock is classified as equity securities with a readily determinable fair value at March 31, 2021. In 2020, the Company also received equity of Zenas BioPharma Limited (Zenas), a private company, in connection with a licensing agreement. The Company elected the measurement alternative to carry the Zenas equity at cost minus impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. There has not been any impairment or observable price changes related to this investment. In 2018, the Company received equity shares in Quellis Biosciences, Inc. (Quellis), a private company, in connection with a licensing transaction. The Company recorded the Quellis equity as securities not having a readily determinable fair value, and the investment was recorded at its original cost. In 2021, Quellis merged into Catabasis Pharmaceuticals, Inc. (Catabasis), and the Company received equity shares in Catabasis, which common shares have a readily determinable fair value. The adjustment in the fair value of the Catabasis equity has been recorded in other income (loss) for the three months ended March 31, 2021. ​ Net gains and losses during the year ended March 31, 2021 and 2020 consist of the following: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended
​ | ​ | March 31,
​ |  | 2021 |  | 2020
Net gains (losses) recognized on equity securities | ​ | $ | 12,981 | ​ | $ | (2,336)
Less: net gains recognized on equity securities redeemed | ​ |  | (1) | ​ |  | —
Unrealized gains (losses) recognized on equity securities | ​ | $ | 12,980 | ​ | $ | (2,336)
​

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