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Financial Instruments (Tables) | 9 Months Ended
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Sep. 30, 2021
Financial Instruments |
Schedule of available-for-sale securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2021 | ​ | December 31, 2020 |
​ |  | Amortized Cost |  | Gross Unrealized Gain |  | Gross Unrealized Loss |  | Estimated Fair Value |  | Amortized Cost |  | Gross Unrealized Gain |  | Gross Unrealized Loss |  | Estimated Fair Value |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | (in thousands) |
Money market deposits | ​ | $ | 55,703 | ​ | $ | — | ​ | $ | — | ​ | $ | 55,703 | ​ | $ | 28,990 | ​ | $ | — | ​ | $ | — | ​ | $ | 28,990 | ​
U.S. Treasury securities (1) | ​ |  | 786,404 | ​ | ​ | 1,821 | ​ | ​ | (350) | ​ |  | 787,875 | ​ |  | 594,252 | ​ |  | 3,512 | ​ |  | (20) | ​ |  | 597,744 | ​
Corporate bonds and notes (1) | ​ |  | 52,868 | ​ | ​ | — | ​ | ​ | (147) | ​ |  | 52,721 | ​ |  | 12,331 | ​ |  | 2 | ​ |  | (5) | ​ |  | 12,328 | ​
Municipal securities | ​ | ​ | 87,824 | ​ | ​ | 378 | ​ | ​ | (202) | ​ | ​ | 88,000 | ​ | ​ | 77,764 | ​ | ​ | 796 | ​ | ​ | (26) | ​ | ​ | 78,534 | ​
Total | ​ | $ | 982,799 | ​ | $ | 2,199 | ​ | $ | (699) | ​ | $ | 984,299 | ​ | $ | 713,337 | ​ | $ | 4,310 | ​ | $ | (51) | ​ | $ | 717,596 | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Classified as: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Cash equivalents (2) | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 55,703 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 28,990 | ​
Short-term investments | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | 928,596 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | 688,606 | ​
Total | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 984,299 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | $ | 717,596 | ​
​
| (1) | Per the Company’s investment policy, all debt securities are classified as short-term investments irrespective of holding period.
| (2) | Cash equivalents includes cash sweep accounts and U.S. Treasury money market mutual funds.
Summarized portfolio of available-for-sale securities by contractual maturity | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2021
​ | ​ | Amortized Cost | ​ | Fair Value
​ | ​ | (in thousands)
Less than or equal to one year | ​ | $ | 403,211 | ​ | $ | 403,784
Greater than one year but less than five years | ​ | ​ | 523,885 | ​ | ​ | 524,812
Total | ​ | $ | 927,096 | ​ | $ | 928,596

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- Definition Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 + Details
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