Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Held to maturity
Due in one year or less, Amortized Cost	$ 32,274,000
Due after one year through five years, Amortized Cost	84,232,000
Due after five years through ten years, Amortized Cost	184,263,000
Due after ten years, Amortized Cost	156,218,000
Mortgage-backed securities, Amortized Cost	30,170,000
Total held to maturity, Amortized Cost	487,156,618	$ 476,093,782
Available for sale
Due in one year or less, Amortized Cost	33,593,000
Due after one year through five years, Amortized Cost	95,836,000
Due after five years through ten years, Amortized Cost	89,588,000
Due after ten years, Amortized Cost	11,408,000
Mortgage-backed securities, Amortized Cost	312,136,000
Total available for sale, Amortized Cost	542,561,000
Held to maturity
Due in one year or less, Estimated Fair Value	32,482,000
Due after one year through five years, Estimated Fair Value	88,324,000
Due after five years through ten years, Estimated Fair Value	191,792,000
Due after ten years, Estimated Fair Value	165,524,000
Mortgage-backed securities, Estimated Fair Value	31,594,000
Total held to maturity, Estimated Fair Value	509,716,000	500,314,000
Available for sale
Due in one year or less, Estimated Fair Value	33,619,000
Due after one year through five years, Estimated Fair Value	97,160,000
Due after five years through ten years, Estimated Fair Value	90,691,000
Due after ten years, Estimated Fair Value	11,836,000
Mortgage-backed securities, Estimated Fair Value	321,157,000
Total available for sale, Estimated Fair Value	$ 554,463,492	$ 564,951,803