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Available-for-Sale Investments (Tables) | 3 Months Ended
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Mar. 31, 2019
Investments Debt And Equity Securities [Abstract] |
Summary of Available-for-Sale Securities Held | The following tables summarize the available-for-sale securities held at March 31, 2019 and December 31, 2018 (in thousands):
March 31, 2019 |  | Amortized cost |  |  | Gross unrealized gains |  |  | Gross unrealized losses |  |  | Fair Value |
Corporate debt securities |  | $ | 90,062 |  |  | $ | 42 |  |  | $ | (3 | ) |  | $ | 90,101 |
U.S. government agency and treasury securities |  | $ | 3,990 |  |  | $ | — |  |  | $ | — |  |  | $ | 3,990 |
Total |  | $ | 94,052 |  |  | $ | 42 |  |  | $ | (3 | ) |  | $ | 94,091 |
December 31, 2018 |  | Amortized cost |  |  | Gross unrealized gains |  |  | Gross unrealized losses |  |  | Fair Value |
Corporate debt securities |  | $ | 107,571 |  |  | $ | 4 |  |  | $ | (70 | ) |  | $ | 107,505 |
U.S. government agency securities |  | $ | 3,971 |  |  | $ | 1 |  |  | $ | — |  |  | $ | 3,972 |
Total |  | $ | 111,542 |  |  | $ | 5 |  |  | $ | (70 | ) |  | $ | 111,477 |

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- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
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