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Marketable Securities (Tables) | 9 Months Ended
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Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract] |
Fair value of marketable securities, by type | The following table summarizes the fair value of our marketable securities, by level within the fair value hierarchy, as of each period end:
| September 30, 2019 |  |  |  |  |  | December 31, 2018 |  |  |  |
| Level 1 |  | Level 2 |  | Total |  | Level 1 |  | Level 2 |  | Total
U.S. Treasury notes and bonds | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 5,034,955 |  |  | $ | — |  |  | $ | 5,034,955 |
Corporate bonds | — |  |  | — |  |  | — |  |  | — |  |  | 2,504,551 |  |  | 2,504,551 |
Commercial paper | — |  |  | 2,265,839 |  | 2,265,839 |  |  | — |  |  | — |  |  | — |
Short-term cash investments | — |  |  | — |  |  | — |  |  | — |  |  | 751,173 |  |  | 751,173 |
Total fair value of marketable securities | $ | — |  |  | $ | 2,265,839 |  |  | $ | 2,265,839 |  |  | $ | 5,034,955 |  |  | $ | 3,255,724 |  |  | $ | 8,290,679 |

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- Definition Tabular disclosure of assets measured at fair value measured on a recurring or nonrecurring basis. Includes, but is not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19190-110258 + Details
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