Investments - Short term invesmtments (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Notes to Financial Statements
U.S. treasury bills	$ 1,148,395	$ 0
U.S. treasury money market fund	0	8,542,292
Custodial trust	6,275,648	0
Commercial paper	499,383	0
Bank money market accounts	2,315,307	562,548
Bank savings accounts	1,763	1,763
Certificates of deposit	200,000	1,098,000
Total short-term investments	$ 10,440,496	$ 10,204,603