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Marketable Securities (Tables)
6 Months Ended
Jun. 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:
June 30, 2019December 31, 2018
Level 1Level 2TotalLevel 1Level 2Total
U.S. Treasury notes and bonds$5,155,696 $— $5,155,696 $5,034,955 $— $5,034,955 
Corporate bonds— — — — 2,504,551 2,504,551 
Commercial paper2,265,824 2,265,824 — — — 
Short-term cash investments— 2,058,166 2,058,166 — 751,173 751,173 
Total fair value of marketable securities$5,155,696 $4,323,990 $9,479,686 $5,034,955 $3,255,724 $8,290,679