Fair Vaule of Financial Instruments - Fair Value of Invested Assets (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
U.S. treasury securities	$ 16,619,619	$ 7,454,225
Corporate securities	40,003,723	28,657,640
Agency mortgage-backed securities	20,286,795	21,737,589
Short-term investments	4,690,954	1,847,778
Total financial instruments	81,601,091	59,697,232
Level 1
U.S. treasury securities	16,619,619	7,454,225
Corporate securities	0	0
Agency mortgage-backed securities	0	0
Short-term investments	4,690,954	1,847,778
Total financial instruments	21,310,573	9,302,003
Level 2
U.S. treasury securities	0	0
Corporate securities	40,003,723	28,657,640
Agency mortgage-backed securities	20,286,795	21,737,589
Short-term investments	0	0
Total financial instruments	60,290,518	50,395,229
Level 3
U.S. treasury securities	0	0
Corporate securities	0	0
Agency mortgage-backed securities	0	0
Short-term investments	0	0
Total financial instruments	$ 0	$ 0