Investments - Short term invesmtments (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Notes to Financial Statements
Short-term U.S. treasury bills	$ 0	$ 4,490,954
Certificates of deposit	200,000	200,000
Total short-term investments	$ 200,000	$ 4,690,954

Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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