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INVESTMENTS | 12 Months Ended
--- | ---
Dec. 31, 2021
INVESTMENTS |
INVESTMENTS | 4. INVESTMENTS The following table summarizes the Company’s investments at: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | Continuous | ​ | Continuous
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​ | Unrealized | ​ | Unrealized
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​ | ​ | Loss Position | ​ | Loss Position
​ | ​ | Amortized | ​ | Holding | ​ | Holding | ​ | Fair | ​ | less than 12 | ​ | greater than 12
December 31, 2021 |  | Cost |  | Gains |  | Losses |  | Value |  | Months |  | Months
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Short-term: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Commercial paper | ​ | $ | 334,077 | ​ | $ | — | ​ | $ | — | ​ | $ | 334,077 | ​ | $ | — | ​ | $ | —
Certificates of deposit | ​ | ​ | 44,502 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 44,502 | ​ | ​ | — | ​ | ​ | —
Municipal securities | ​ |  | 666 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 666 | ​ | ​ | — | ​ | ​ | —
U.S. government agency securities | ​ |  | 62,687 | ​ |  | — | ​ |  | 26 | ​ |  | 62,661 | ​ |  | 26 | ​ |  | —
U.S. treasuries | ​ | ​ | 1,308,536 | ​ |  | 2 | ​ |  | 717 | ​ |  | 1,307,821 | ​ |  | 717 | ​ |  | —
Long-term: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agency securities | ​ | ​ | 12,500 | ​ | ​ | — | ​ | ​ | 24 | ​ | ​ | 12,476 | ​ | ​ | 24 | ​ | ​ | —
U.S. treasuries | ​ | ​ | 87,133 | ​ | ​ | — | ​ | ​ | 190 | ​ | ​ | 86,943 | ​ | ​ | 190 | ​ | ​ | —
Total | ​ | $ | 1,850,101 | ​ | $ | 2 | ​ | $ | 957 | ​ | $ | 1,849,146 | ​ | $ | 957 | ​ | $ | —
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | Continuous | ​ | Continuous
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​ | ​ | Unrealized | ​ | Unrealized
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | Unrealized | ​ | ​ | ​ | ​ | Loss Position | ​ | Loss Position
​ | ​ | Amortized | ​ | Holding | ​ | Holding | ​ | Fair | ​ | less than 12 | ​ | greater than 12
December 31, 2020 |  | Cost |  | Gains |  | Losses |  | Value |  | Months |  | Months
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Short-term: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Commercial paper | ​ | $ | 119,886 | ​ | $ | — | ​ | $ | — | ​ | $ | 119,886 | ​ | $ | — | ​ | $ | —
Certificates of deposit | ​ | ​ | 20,387 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 20,387 | ​ | ​ | — | ​ | ​ | —
Municipal securities | ​ |  | 9,083 | ​ |  | — | ​ |  | — | ​ |  | 9,083 | ​ |  | — | ​ |  | —
U.S. government agency securities | ​ |  | 81,521 | ​ |  | 13 | ​ |  | 3 | ​ |  | 81,531 | ​ |  | 3 | ​ |  | —
U.S. treasuries | ​ | ​ | 650,386 | ​ | ​ | 150 | ​ | ​ | 69 | ​ | ​ | 650,467 | ​ | ​ | 69 | ​ | ​ | —
Long-term: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agency securities | ​ | ​ | 10,350 | ​ | ​ | 1 | ​ | ​ | — | ​ | ​ | 10,351 | ​ | ​ | — | ​ | ​ | —
U.S. treasuries | ​ | ​ | 33,946 | ​ | ​ | 1 | ​ | ​ | 7 | ​ | ​ | 33,940 | ​ | ​ | 7 | ​ | ​ | —
Total | ​ | $ | 925,559 | ​ | $ | 165 | ​ | $ | 79 | ​ | $ | 925,645 | ​ | $ | 79 | ​ | $ | —
​ During the years ended December 31, 2021, 2020 and 2019, realized gains or losses recognized on the sale of investments were not significant. The Company’s investments at December 31, 2021 and 2020 carried investment grade credit ratings. The following table summarizes the underlying contractual maturities of the Company’s investments at:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2021 | ​ | December 31, 2020
​ |  | Amortized Cost |  | Fair Value |  | Amortized Cost |  | Fair Value
Less than 1 year: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Commercial paper | ​ | $ | 334,077 | ​ | $ | 334,077 |  | $ | 119,886 | ​ | $ | 119,886
Municipal securities | ​ |  | 666 | ​ |  | 666 |  |  | 9,083 | ​ |  | 9,083
U.S. government agency securities | ​ |  | 62,687 | ​ |  | 62,661 |  |  | 81,521 | ​ |  | 81,531
Certificates of deposit | ​ |  | 44,502 | ​ |  | 44,502 |  |  | 20,387 | ​ |  | 20,387
U.S. treasuries | ​ | ​ | 1,308,536 | ​ | ​ | 1,307,821 | ​ | ​ | 650,386 | ​ | ​ | 650,467
Due 1 - 10 years: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. treasuries | ​ | ​ | 87,133 | ​ | ​ | 86,943 | ​ | ​ | 33,946 | ​ | ​ | 33,940
U.S. government agency securities | ​ |  | 12,500 | ​ |  | 12,476 |  |  | 10,350 | ​ |  | 10,351
Total | ​ | $ | 1,850,101 | ​ | $ | 1,849,146 |  | $ | 925,559 | ​ | $ | 925,645
​

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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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