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Fair Value Measurements (Detail) - Fair Value Measurements at Reporting Date Using - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Investment Securities | $ 672,463 | $ 401,132
Short-term investments |  |
Investment Securities | 532,477 | 335,928
Long-term investments |  |
Investment Securities | 0 | 15,542
Fair Value, Inputs, Level 1 |  |
Investment Securities | 5,340 | 42,653
Fair Value, Inputs, Level 1 | Short-term investments |  |
Investment Securities | 0 | 0
Fair Value, Inputs, Level 1 | Long-term investments |  |
Investment Securities | 0 | 0
Fair Value, Inputs, Level 2 |  |
Investment Securities | 667,123 | 358,479
Fair Value, Inputs, Level 2 | Short-term investments |  |
Investment Securities | 532,477 | 335,928
Fair Value, Inputs, Level 2 | Long-term investments |  |
Investment Securities | 0 | 15,542
Commercial paper | Short-term investments |  |
Investment Securities | 229,821 | 161,286
Commercial paper | Fair Value, Inputs, Level 1 | Short-term investments |  |
Investment Securities | 0 | 0
Commercial paper | Fair Value, Inputs, Level 2 | Short-term investments |  |
Investment Securities | 229,821 | 161,286
US Government Corporations and Agencies Securities | Short-term investments |  |
Investment Securities | 48,598 | 13,515
US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 1 | Short-term investments |  |
Investment Securities | 0 | 0
US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 2 | Short-term investments |  |
Investment Securities | 48,598 | 13,515
US Treasury Securities | Short-term investments |  |
Investment Securities | 0 | 2,915
US Treasury Securities | Long-term investments |  |
Investment Securities | 0 | 146
US Treasury Securities | Fair Value, Inputs, Level 1 | Short-term investments |  |
Investment Securities | 0 | 0
US Treasury Securities | Fair Value, Inputs, Level 1 | Long-term investments |  |
Investment Securities | 0 | 0
US Treasury Securities | Fair Value, Inputs, Level 2 | Short-term investments |  |
Investment Securities | 0 | 2,915
US Treasury Securities | Fair Value, Inputs, Level 2 | Long-term investments |  |
Investment Securities | 0 | 146
Municipal debt securities | Short-term investments |  |
Investment Securities | 87,290 | 12,237
Municipal debt securities | Fair Value, Inputs, Level 1 | Short-term investments |  |
Investment Securities | 0 | 0
Municipal debt securities | Fair Value, Inputs, Level 2 | Short-term investments |  |
Investment Securities | 87,290 | 12,237
Corporate debt securities | Short-term investments |  |
Investment Securities | 166,768 | 145,975
Corporate debt securities | Long-term investments |  |
Investment Securities | 0 | 15,396
Corporate debt securities | Fair Value, Inputs, Level 1 | Short-term investments |  |
Investment Securities | 0 | 0
Corporate debt securities | Fair Value, Inputs, Level 1 | Long-term investments |  |
Investment Securities | 0 | 0
Corporate debt securities | Fair Value, Inputs, Level 2 | Short-term investments |  |
Investment Securities | 166,768 | 145,975
Corporate debt securities | Fair Value, Inputs, Level 2 | Long-term investments |  |
Investment Securities | 0 | 15,396
Cash Equivalents |  |
Cash Equivalents | 139,986 | 49,662
Cash Equivalents | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 5,340 | 42,653
Cash Equivalents | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 134,646 | 7,009
Cash Equivalents | Money market funds |  |
Cash Equivalents | 5,340 | 42,653
Cash Equivalents | Money market funds | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 5,340 | 42,653
Cash Equivalents | Money market funds | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | Commercial paper |  |
Cash Equivalents | 48,908 | 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 | 48,908 | 5,807
Cash Equivalents | US Government Corporations and Agencies Securities |  |
Cash Equivalents | 51,400 | 0
Cash Equivalents | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 1 |  |
Cash Equivalents | 0 | 0
Cash Equivalents | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 2 |  |
Cash Equivalents | 51,400 | 0
Cash Equivalents | Municipal debt securities |  |
Cash Equivalents | 34,338 | 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 | $ 34,338 | $ 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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