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Cash and Cash Equivalents and Short-Term Investments (Tables) | 6 Months Ended
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Jun. 30, 2019
Cash and Cash Equivalents [Abstract] |
Summary of amortized cost, unrealized gain and loss and estimated fair value | The following tables summarize the amortized cost, unrealized gain and loss and estimated fair value of cash equivalents and short-term investments:
| June 30, 2019
(in thousands) | Amortized Cost |  | Unrealized Gain |  | Unrealized Loss |  | Estimated Fair Value
Cash equivalents: |  |  |  |  |  |  |
Money market funds | $ | 37,659 |  |  | $ | — |  |  | $ | — |  |  | $ | 37,659 |
Commercial paper | 9,094 |  |  | — |  |  | — |  |  | 9,094 |
Total cash equivalents | $ | 46,753 |  |  | $ | — |  |  | $ | — |  |  | $ | 46,753 |
Short-term investments: |  |  |  |  |  |  |
Commercial paper | $ | 46,220 |  |  | $ | — |  |  | $ | — |  |  | $ | 46,220 |
Corporate bonds | 20,219 |  |  | 37 |  |  | — |  |  | 20,256 |
U.S. Treasury and agency obligations | 44,782 |  |  | 43 |  |  | — |  |  | 44,825 |
Total short-term investments | $ | 111,221 |  |  | $ | 80 |  |  | $ | — |  |  | $ | 111,301 |
| December 31, 2018
(in thousands) | Amortized Cost |  | Unrealized Gain |  | Unrealized Loss |  | Estimated Fair Value
Cash equivalents: |  |  |  |  |  |  |
Money market funds | $ | 38,022 |  |  | $ | — |  |  | $ | — |  |  | $ | 38,022 |
Total cash equivalents | $ | 38,022 |  |  | $ | — |  |  | $ | — |  |  | $ | 38,022 |
Short-term investments: |  |  |  |  |  |  |
Commercial paper | $ | 79,634 |  |  | $ | — |  |  | $ | — |  |  | $ | 79,634 |
Corporate bonds | 16,119 |  |  | — |  |  | — |  |  | 16,119 |
U.S. Treasury and agency obligations | 22,366 |  |  | — |  |  | — |  |  | 22,366 |
Total short-term investments | $ | 118,119 |  |  | $ | — |  |  | $ | — |  |  | $ | 118,119 |

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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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