Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Held to maturity
Due in one year or less, Amortized Cost	$ 500,000
Due after one year through five years, Amortized Cost	28,800,000
Due after five years through ten years, Amortized Cost	4,956,000
Due after ten years, Amortized Cost
Residential mortgage-backed securities, Amortized Cost	115,000
Total held to maturity, Amortized Cost	34,371,191	42,100,196
Due in one year or less, Estimated Fair Value	500,000
Due after one year through five years, Estimated Fair Value	29,566,000
Due after five years through ten years, Estimated Fair Value	5,099,000
Due after ten years, Estimated Fair Value
Residential mortgage-backed securities, Estimated Fair Value	122,000
Total held to maturity, Estimated Fair Value	35,287,000	43,736,000
Available for sale
Due in one year or less, Amortized Cost	11,055,000
Due after one year through five years, Amortized Cost	55,883,000
Due after five years through ten years, Amortized Cost	216,350,000
Due after ten years, Amortized Cost	271,689,000
Residential mortgage-backed securities, Amortized Cost	121,757,000
Total available for sale, Amortized Cost	676,734,000
Due in one year or less, Estimated Fair Value	11,215,000
Due after one year through five years, Estimated Fair Value	56,907,000
Due after five years through ten years, Estimated Fair Value	219,694,000
Due after ten years, Estimated Fair Value	270,690,000
Residential mortgage-backed securities, Estimated Fair Value	120,532,000
Total available for sale, Estimated Fair Value	$ 679,037,599	$ 694,509,821