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Cash, cash equivalents and short-term investments (Tables) | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |  |
Summary of cash, cash equivalents and short-term investments | The following tables summarize our cash, cash equivalents and short-term investments as of June 30, 2018 and December 31, 2017 (in thousands):
June 30, 2018 |  | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Cash and money market funds |  | $ | 24,601 |  |  | $ | — |  |  | $ | — |  |  | $ | 24,601 |
Corporate debt |  |  |  |  |  |  |  |  |  |  |  |
Due in one year or less |  | 21,054 |  |  | — |  |  | (8 | ) |  | 21,046 |
U.S. government securities |  |  |  |  |  |  |  |
Due in one year or less |  | 7,982 |  |  | — |  |  | (1 | ) |  | 7,981 |
Total |  | $ | 53,637 |  |  | $ | — |  |  | $ | (9 | ) |  | $ | 53,628 |
Reported as: |  |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  | $ | 24,601 |  |  | $ | — |  |  | $ | — |  |  | $ | 24,601 |
Short-term investments |  | 29,036 |  |  | — |  |  | (9 | ) |  | 29,027 |
Total |  | $ | 53,637 |  |  | $ | — |  |  | $ | (9 | ) |  | $ | 53,628 |
December 31, 2017 |  | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Cash and money market funds |  | $ | 15,703 |  |  | $ | — |  |  | $ | — |  |  | $ | 15,703 |
Corporate debt |  |  |  |  |  |  |  |  |  |  |  |
Due in one year or less |  | 38,053 |  |  | — |  |  | (21 | ) |  | 38,032 |
U.S. government securities |  |  |  |  |  |  |  |
Due in one year or less |  | 13,474 |  |  | — |  |  | (6 | ) |  | 13,468 |
Total |  | $ | 67,230 |  |  | $ | — |  |  | $ | (27 | ) |  | $ | 67,203 |
Reported as: |  |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  | $ | 15,703 |  |  | $ | — |  |  | $ | — |  |  | $ | 15,703 |
Short-term investments |  | 51,527 |  |  | — |  |  | (27 | ) |  | 51,500 |
Total |  | $ | 67,230 |  |  | $ | — |  |  | $ | (27 | ) |  | $ | 67,203 |
| The following tables summarize our cash, cash equivalents and short-term investments as of December 31, 2017 and 2016 (in thousands):
December 31, 2017 | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Cash and money market funds | $ | 15,703 |  |  | $ | — |  |  | $ | — |  |  | $ | 15,703 |
Corporate debt securities: |  |  |  |  |  |  |
Due in one year or less | 38,053 |  |  | — |  |  | (21 | ) |  | 38,032 |
U.S. government securities: |  |  |  |  |  |  |
Due in one year or less | 13,474 |  |  | — |  |  | (6 | ) |  | 13,468 |
Total | $ | 67,230 |  |  | $ | — |  |  | $ | (27 | ) |  | $ | 67,203 |
Reported as: |  |  |  |  |  |  |
Cash and cash equivalents | $ | 15,703 |  |  | $ | — |  |  | $ | — |  |  | $ | 15,703 |
Short-term investments | 51,527 |  |  | — |  |  | (27 | ) |  | 51,500 |
Total | $ | 67,230 |  |  | $ | — |  |  | $ | (27 | ) |  | $ | 67,203 |
December 31, 2016 | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Cash and money market funds | $ | 43,930 |  |  | $ | — |  |  | $ | — |  |  | $ | 43,930 |
Corporate debt securities: |  |  |  |  |  |  |
Due in one year or less | 48,492 |  |  | 3 |  |  | (29 | ) |  | 48,466 |
U.S. government securities: |  |  |  |  |  |  |
Due in one year or less | 14,013 |  |  | — |  |  | (16 | ) |  | 13,997 |
Due in two years or less | 8,013 |  |  | — |  |  | (18 | ) |  | 7,995 |
Total | $ | 114,448 |  |  | $ | 3 |  |  | $ | (63 | ) |  | $ | 114,388 |
Reported as: |  |  |  |  |  |  |
Cash and cash equivalents | $ | 43,930 |  |  | $ | — |  |  | $ | — |  |  | $ | 43,930 |
Short-term investments | 70,518 |  |  | 3 |  |  | (63 | ) |  | 70,458 |
Total | $ | 114,448 |  |  | $ | 3 |  |  | $ | (63 | ) |  | $ | 114,388 |

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