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Investments (Tables) | 12 Months Ended
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Dec. 31, 2017
Investments |
Summary of fair value and unrealized gains (losses) position of available for sale securities |
|  |  |  | Gross |  | Gross |  |  |
|  | Amortized |  | Unrealized |  | Unrealized |  | Estimated |
|  | Cost |  | Gains |  | Losses |  | Fair Value |
|  | (in thousands) |
December 31, 2017 |  |  |  |  |  |  |  |  |
U.S. treasuries |  | $ | 33,914 |  | $ | — |  | $ | (19 | ) | $ | 33,895 |
Corporate debt |  | 10,894 |  | — |  | (8 | ) | 10,886 |
Commercial paper |  | 2,999 |  | — |  | — |  | 2,999 |
Total |  | $ | 47,807 |  | $ | — |  | $ | (27 | ) | $ | 47,780 |
December 31, 2016 |  |  |  |  |  |  |  |  |
U.S. treasuries |  | $ | 40,013 |  | $ | — |  | $ | (5 | ) | $ | 40,008 |
Government agency securities |  | 10,020 |  | — |  | (8 | ) | 10,012 |
Corporate debt |  | 13,780 |  | — |  | (7 | ) | 13,773 |
Commercial paper |  | 2,994 |  | — |  | — |  | 2,994 |
Total |  | $ | 66,807 |  | $ | — |  | $ | (20 | ) | $ | 66,787 |
Summary of fair value and unrealized losses of available-for-sale securities in a loss position |
|  | December 31, 2017 |  | December 31, 2016 |
|  |  |  | Gross |  |  |  | Gross |
|  | Estimated |  | Unrealized |  | Estimated |  | Unrealized |
|  | Fair Value |  | Losses |  | Fair Value |  | Losses |
|  | (in thousands) |
U.S. treasuries |  | $ | 33,895 |  | $ | (19 | ) | $ | 20,002 |  | $ | (5 | )
Government agency securities |  | — |  | — |  | 10,012 |  | (8 | )
Corporate debt |  | 10,886 |  | (8 | ) | 13,773 |  | (7 | )
Total |  | $ | 44,781 |  | $ | (27 | ) | $ | 43,787 |  | $ | (20 | )

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- Definition Tabular disclosure of fair value of investments in debt and equity securities in an unrealized loss position categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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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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