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Marketable Securities (Tables) | 12 Months Ended
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Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract] |
Available-for-sale securities | Marketable securities consisted of the following as of December 31, 2018 and 2017:
December 31, 2018 | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Money market mutual funds | $ | 25 |  |  | $ | — |  |  | $ | — |  |  | $ | 25 |
Total marketable securities designated as available-for-sale | $ | 25 |  |  | $ | — |  |  | $ | — |  |  | $ | 25 |
December 31, 2017 | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value
Money market mutual funds | $ | 7,318 |  |  | $ | — |  |  | $ | — |  |  | $ | 7,318 |
United States treasuries | 1,002 |  |  | — |  |  | (1 | ) |  | 1,001 |
Total marketable securities designated as available-for-sale | $ | 8,320 |  |  | $ | — |  |  | $ | (1 | ) |  | $ | 8,319 |
Available-for-sale securities, debt maturities, amortized cost and fair value basis | The amortized costs and fair value of debt securities as of December 31, 2018 and 2017 are shown below by effective maturity. Effective maturities may differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties.
December 31, 2018 | Amortized Cost |  | Fair Value
Due in less than one year | $ | — |  |  | $ | — |
December 31, 2017 | Amortized Cost |  | Fair Value
Due in less than one year | $ | 1,002 |  |  | $ | 1,001 |

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- Definition Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 + Details
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- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
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