Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Held to maturity
Due in one year or less, Amortized Cost	$ 4,096,270
Due after one year through five years, Amortized Cost	57,702,099
Due after five years through ten years, Amortized Cost	118,294,836
Due after ten years, Amortized Cost	137,249,171
Mortgage-backed securities, Amortized Cost	49,312,701
Total held to maturity, Amortized Cost	366,655,077	$ 336,100,948
Available for sale
Due in one year or less, Amortized Cost	49,257,873
Due after one year through five years, Amortized Cost	97,814,378
Due after five years through ten years, Amortized Cost	103,015,782
Due after ten years, Amortized Cost	28,403,543
Mortgage-backed securities, Amortized Cost	259,922,761
Total available for sale, Amortized Cost	538,414,337	511,629,644
Held to maturity
Due in one year or less, Estimated Fair Value	4,090,120
Due after one year through five years, Estimated Fair Value	58,997,125
Due after five years through ten years, Estimated Fair Value	121,747,801
Due after ten years, Estimated Fair Value	145,943,343
Mortgage-backed securities, Estimated Fair Value	49,672,039
Total held to maturity, Estimated Fair Value	380,450,428	344,647,138
Available for sale
Due in one year or less, Estimated Fair Value	49,729,548
Due after one year through five years, Estimated Fair Value	98,914,332
Due after five years through ten years, Estimated Fair Value	103,609,213
Due after ten years, Estimated Fair Value	29,652,920
Mortgage-backed securities, Estimated Fair Value	257,040,037
Total available for sale, Estimated Fair Value	$ 538,946,050	$ 515,074,940