Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Held to maturity
Due in one year or less, Amortized Cost	$ 9,643,000
Due after one year through five years, Amortized Cost	42,967,000
Due after five years through ten years, Amortized Cost	86,925,000
Due after ten years, Amortized Cost	128,504,000
Mortgage-backed securities, Amortized Cost	64,234,000
Total held to maturity, Amortized Cost	332,272,969	$ 310,258,704
Available for sale
Due in one year or less, Amortized Cost	36,476,000
Due after one year through five years, Amortized Cost	115,204,000
Due after five years through ten years, Amortized Cost	105,689,000
Due after ten years, Amortized Cost	51,534,000
Mortgage-backed securities, Amortized Cost	190,936,000
Total available for sale, Amortized Cost	499,839,000
Held to maturity
Due in one year or less, Estimated Fair Value	9,657,000
Due after one year through five years, Estimated Fair Value	44,275,000
Due after five years through ten years, Estimated Fair Value	92,926,000
Due after ten years, Estimated Fair Value	141,354,000
Mortgage-backed securities, Estimated Fair Value	66,659,000
Total held to maturity, Estimated Fair Value	354,871,000	322,799,000
Available for sale
Due in one year or less, Estimated Fair Value	37,158,000
Due after one year through five years, Estimated Fair Value	119,709,000
Due after five years through ten years, Estimated Fair Value	109,631,000
Due after ten years, Estimated Fair Value	54,994,000
Mortgage-backed securities, Estimated Fair Value	194,329,000
Total available for sale, Estimated Fair Value	$ 515,821,393	$ 501,393,559