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Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Available-for-sale Securities | $ 675,824 | $ 672,463
Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 160,730 | 5,340
Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 515,094 | 667,123
Short-term Investments |  |
Available-for-sale Securities | 426,381 | 532,477
Short-term Investments | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Short-term Investments | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 426,381 | 532,477
Short-term Investments | Commercial paper |  |
Available-for-sale Securities | 188,937 | 229,821
Short-term Investments | Commercial paper | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Short-term Investments | Commercial paper | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 188,937 | 229,821
Short-term Investments | Municipal debt securities |  |
Available-for-sale Securities | 84,294 | 87,290
Short-term Investments | Municipal debt securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Short-term Investments | Municipal debt securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 84,294 | 87,290
Short-term Investments | Corporate debt securities |  |
Available-for-sale Securities | 115,812 | 166,768
Short-term Investments | Corporate debt securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Short-term Investments | Corporate debt securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 115,812 | 166,768
Short-term Investments | US Treasury Bond Securities |  |
Available-for-sale Securities | 37,338 | 48,598
Short-term Investments | US Treasury Bond Securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Short-term Investments | US Treasury Bond Securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 37,338 | 48,598
Cash Equivalents |  |
Cash Equivalents | 249,443 | 139,986
Cash Equivalents | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 160,730 | 5,340
Cash Equivalents | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 88,713 | 134,646
Cash Equivalents | Money Market Funds |  |
Cash Equivalents | 160,730 | 5,340
Cash Equivalents | Money Market Funds | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 160,730 | 5,340
Cash Equivalents | Money Market Funds | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Commercial paper |  |
Cash Equivalents | 21,889 | 48,908
Cash Equivalents | Commercial paper | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Commercial paper | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 21,889 | 48,908
Cash Equivalents | Municipal debt securities |  |
Cash Equivalents | 59,417 | 34,338
Cash Equivalents | Municipal debt securities | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Municipal debt securities | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 59,417 | 34,338
Cash Equivalents | Federal agency debt securities |  |
Cash Equivalents | 0 | 51,400
Cash Equivalents | Federal agency debt securities | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Federal agency debt securities | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 0 | 51,400
Cash Equivalents | Corporate debt securities |  |
Cash Equivalents | 7,407 | 0
Cash Equivalents | Corporate debt securities | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Corporate debt securities | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | $ 7,407 | $ 0

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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