Investments, Debt Securities by Contractual Maturity (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Amortized cost of debt securities, by contractual maturity [Abstract]
Due in one year or less	$ 4,996,905
Due after one year through five years	30,412,755
Due after five years through ten years	60,548,458
Due after ten years	63,629,308
Original or amortized cost	159,587,426	$ 159,912,511
Estimated fair value of debt securities, by contractual maturity [Abstract]
Due in one year or less	5,084,620
Due after one year through five years	34,408,309
Due after five years through ten years	60,929,783
Due after ten years	61,619,811
Estimated fair value	$ 162,042,523	$ 178,555,225	[1]

[1] Balance sheet audited at December 31, 2017.