v3.10.0.1
Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)
Sep. 30, 2018
Dec. 31, 2017
Held to maturity    
Due in one year or less, Amortized Cost $ 8,783,000  
Due after one year through five years, Amortized Cost 70,790,000  
Due after five years through ten years, Amortized Cost 136,673,000  
Due after ten years, Amortized Cost 141,766,000  
Mortgage-backed securities, Amortized Cost 42,221,000  
Total held to maturity, Amortized Cost 400,233,054 $ 366,655,077
Available for sale    
Due in one year or less, Amortized Cost 39,265,000  
Due after one year through five years, Amortized Cost 86,468,000  
Due after five years through ten years, Amortized Cost 116,791,000  
Due after ten years, Amortized Cost 19,261,000  
Mortgage-backed securities, Amortized Cost 276,973,000  
Total available for sale, Amortized Cost 538,758,000  
Held to maturity    
Due in one year or less, Estimated Fair Value 8,768,000  
Due after one year through five years, Estimated Fair Value 70,505,000  
Due after five years through ten years, Estimated Fair Value 135,068,000  
Due after ten years, Estimated Fair Value 142,645,000  
Mortgage-backed securities, Estimated Fair Value 41,188,000  
Total held to maturity, Estimated Fair Value 398,174,000 380,450,000
Available for sale    
Due in one year or less, Estimated Fair Value 39,465,000  
Due after one year through five years, Estimated Fair Value 85,156,000  
Due after five years through ten years, Estimated Fair Value 114,026,000  
Due after ten years, Estimated Fair Value 19,337,000  
Mortgage-backed securities, Estimated Fair Value 267,043,000  
Total available for sale, Estimated Fair Value $ 525,027,434 $ 538,946,050