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Marketable Securities | 12 Months Ended
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Dec. 31, 2021
Marketable Securities |
Marketable Securities | (5) Marketable Securities The following is a summary of marketable debt securities, classified as available-for-sale: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ | ​ |  | Gross |  | Gross |  | ​ | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | Fair
​ | ​ | Cost | ​ | Gains | ​ | Losses | ​ | Value
​ | ​ | (In thousands)
December 31, 2021 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Marketable securities | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government and municipal obligations | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Maturing in one year or less | ​ | $ | 80,674 | ​ | $ | — | ​ | $ | (133) | ​ | $ | 80,541
Maturing after one year through three years | ​ | ​ | 51,319 | ​ | ​ | — | ​ | ​ | (184) | ​ | ​ | 51,135
Total U.S. government and municipal obligations | ​ | $ | 131,993 | ​ | $ | — | ​ | $ | (317) | ​ | $ | 131,676
Corporate debt securities | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Maturing in one year or less | ​ | $ | 170,034 | ​ | $ | — | ​ | $ | (28) | ​ | $ | 170,006
Maturing after one year through three years | ​ | ​ | 67,782 | ​ | ​ | — | ​ | ​ | (357) | ​ | ​ | 67,425
Total corporate debt securities | ​ | $ | 237,816 | ​ | $ | — | ​ | $ | (385) | ​ | $ | 237,431
Total marketable securities | ​ | $ | 369,809 | ​ | $ | — | ​ | $ | (702) | ​ | $ | 369,107
December 31, 2020 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Marketable securities | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government and municipal obligations | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Maturing in one year or less | ​ | $ | 40,328 | ​ | $ | 3 | ​ | $ | (2) | ​ | $ | 40,329
Maturing after one year through three years | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Total U.S. government and municipal obligations | ​ | $ | 40,328 | ​ | $ | 3 | ​ | $ | (2) | ​ | $ | 40,329
Corporate debt securities | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Maturing in one year or less | ​ | $ | 110,265 | ​ | $ | 2 | ​ | $ | (10) | ​ | $ | 110,257
Maturing after one year through three years | ​ | ​ | — | ​ | ​ | — | ​ | ​ | — | ​ | ​ | —
Total corporate debt securities | ​ | $ | 110,265 | ​ | $ | 2 | ​ | $ | (10) | ​ | $ | 110,257
Total marketable securities | ​ | $ | 150,593 | ​ | $ | 5 | ​ | $ | (12) | ​ | $ | 150,586
​ The Company holds investment grade marketable securities, and none were considered to be other-than-temporarily impaired as of December 31, 2021. Marketable securities include $1.3 million and $0.2 million in accrued interest at December 31, 2021 and December 31, 2020, respectively.

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- Definition The entire disclosure for investments in certain debt and equity securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2209399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2324412 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2176304 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1403 -Paragraph (b) + Details
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