Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Held to maturity
Due in one year or less, Amortized Cost	$ 10,830,000
Due after one year through five years, Amortized Cost	51,254,000
Due after five years through ten years, Amortized Cost	131,295,000
Due after ten years, Amortized Cost	101,425,000
Mortgage-backed securities, Amortized Cost	57,492,000
Total held to maturity, Amortized Cost	352,296,461	$ 336,100,948
Available for sale
Due in one year or less, Amortized Cost	76,426,000
Due after one year through five years, Amortized Cost	88,029,000
Due after five years through ten years, Amortized Cost	97,313,000
Due after ten years, Amortized Cost	37,223,000
Mortgage-backed securities, Amortized Cost	208,865,000
Total available for sale, Amortized Cost	507,856,000
Held to maturity
Due in one year or less, Estimated Fair Value	10,850,000
Due after one year through five years, Estimated Fair Value	52,381,000
Due after five years through ten years, Estimated Fair Value	134,235,000
Due after ten years, Estimated Fair Value	106,783,000
Mortgage-backed securities, Estimated Fair Value	58,047,000
Total held to maturity, Estimated Fair Value	362,296,000	344,647,000
Available for sale
Due in one year or less, Estimated Fair Value	78,276,000
Due after one year through five years, Estimated Fair Value	89,498,000
Due after five years through ten years, Estimated Fair Value	97,917,000
Due after ten years, Estimated Fair Value	38,716,000
Mortgage-backed securities, Estimated Fair Value	206,762,000
Total available for sale, Estimated Fair Value	$ 511,168,645	$ 515,074,940