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Available-for-Sale Investments (Tables) | 12 Months Ended
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Dec. 31, 2018
Investments Debt And Equity Securities [Abstract] |
Summary of Available-for-Sale Securities Held | The following tables summarize the available-for-sale securities held at December 31, 2018 and 2017 (in thousands):
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 |
December 31, 2017 |  | Amortized cost |  |  | Gross unrealized gains |  |  | Gross unrealized losses |  |  | Fair Value |
Corporate debt securities |  | $ | 28,593 |  |  | $ | 1 |  |  | $ | (9 | ) |  | $ | 28,585 |
Total |  | $ | 28,593 |  |  | $ | 1 |  |  | $ | (9 | ) |  | $ | 28,585 |

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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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