Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Held to maturity
Due in one year or less, Amortized Cost	$ 9,703,000
Due after one year through five years, Amortized Cost	42,968,000
Due after five years through ten years, Amortized Cost	85,940,000
Due after ten years, Amortized Cost	121,299,000
Mortgage-backed securities, Amortized Cost	68,257,000
Total held to maturity, Amortized Cost	328,166,897	$ 310,258,704
Due in one year or less, Estimated Fair Value	40,729,000
Due after one year through five years, Estimated Fair Value	100,924,000
Due after five years through ten years, Estimated Fair Value	108,579,000
Due after ten years, Estimated Fair Value	60,240,000
Mortgage-backed securities, Estimated Fair Value	181,222,000
Total held to maturity, Estimated Fair Value	352,864,000	322,799,000
Available for sale
Due in one year or less, Amortized Cost	9,733,000
Due after one year through five years, Amortized Cost	44,547,000
Due after five years through ten years, Amortized Cost	92,360,000
Due after ten years, Amortized Cost	135,297,000
Mortgage-backed securities, Amortized Cost	70,927,000
Total available for sale, Amortized Cost	352,864,000
Due in one year or less, Estimated Fair Value	41,748,000
Due after one year through five years, Estimated Fair Value	105,002,000
Due after five years through ten years, Estimated Fair Value	113,634,000
Due after ten years, Estimated Fair Value	64,735,000
Mortgage-backed securities, Estimated Fair Value	184,990,000
Total available for sale, Estimated Fair Value	$ 510,108,845	$ 501,393,559