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Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Mar. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Available-for-sale Securities | $ 385,421 | $ 401,132
Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 47,774 | 42,653
Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 337,647 | 358,479
Short-term Investments |  |
Available-for-sale Securities | 314,946 | 335,928
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 | 314,946 | 335,928
Short-term Investments | Commercial paper |  |
Available-for-sale Securities | 142,667 | 161,286
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 | 142,667 | 161,286
Short-term Investments | Municipal debt securities |  |
Available-for-sale Securities | 8,678 | 12,237
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 | 8,678 | 12,237
Short-term Investments | Federal agency debt securities |  |
Available-for-sale Securities | 2,465 | 13,515
Short-term Investments | Federal agency debt securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Short-term Investments | Federal agency debt securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 2,465 | 13,515
Short-term Investments | Corporate debt securities |  |
Available-for-sale Securities | 158,060 | 145,975
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 | 158,060 | 145,975
Short-term Investments | US Treasury Bond Securities |  |
Available-for-sale Securities | 3,076 | 2,915
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 | 3,076 | 2,915
Long Term Investments |  |
Available-for-sale Securities | 11,019 | 15,542
Long Term Investments | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Long Term Investments | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 11,019 | 15,542
Long Term Investments | Federal agency debt securities |  |
Available-for-sale Securities | 11,019 | 0
Long Term Investments | Federal agency debt securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Long Term Investments | Federal agency debt securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 11,019 | 0
Long Term Investments | Corporate debt securities |  |
Available-for-sale Securities | 0 | 15,396
Long Term Investments | Corporate debt securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Long Term Investments | Corporate debt securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 0 | 15,396
Long Term Investments | US Treasury Bond Securities |  |
Available-for-sale Securities | 0 | 146
Long Term Investments | US Treasury Bond Securities | Fair Value, Inputs, Level 1 |  |
Available-for-sale Securities | 0 | 0
Long Term Investments | US Treasury Bond Securities | Fair Value, Inputs, Level 2 |  |
Available-for-sale Securities | 0 | 146
Cash Equivalents |  |
Cash Equivalents | 59,456 | 49,662
Cash Equivalents | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 47,774 | 42,653
Cash Equivalents | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 11,682 | 7,009
Cash Equivalents | Money Market Funds |  |
Cash Equivalents | 47,774 | 42,653
Cash Equivalents | Money Market Funds | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 47,774 | 42,653
Cash Equivalents | Money Market Funds | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Commercial paper |  |
Cash Equivalents | 7,135 | 5,807
Cash Equivalents | Commercial paper | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Commercial paper | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 7,135 | 5,807
Cash Equivalents | Municipal debt securities |  |
Cash Equivalents | 4,547 | 1,202
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 | $ 4,547 | $ 1,202

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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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