Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities by Contractual Maturity (Detail) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Held to maturity
Due in one year or less, Amortized Cost	$ 3,787,000
Due after one year through five years, Amortized Cost	35,943,000
Due after five years through ten years, Amortized Cost	76,046,000
Due after ten years, Amortized Cost	100,037,000
Mortgage-backed securities, Amortized Cost	82,498,000
Total held to maturity, Amortized Cost	298,310,713	$ 307,391,699
Due in one year or less, Estimated Fair Value	3,782,000
Due after one year through five years, Estimated Fair Value	36,539,000
Due after five years through ten years, Estimated Fair Value	77,971,000
Due after ten years, Estimated Fair Value	105,657,000
Mortgage-backed securities, Estimated Fair Value	83,694,000
Total held to maturity, Estimated Fair Value	307,643,000	322,155,000
Available for sale
Due in one year or less, Amortized Cost	29,336,000
Due after one year through five years, Amortized Cost	89,359,000
Due after five years through ten years, Amortized Cost	114,226,000
Due after ten years, Amortized Cost	111,914,000
Mortgage-backed securities, Amortized Cost	112,497,000
Total available for sale, Amortized Cost	457,332,000
Due in one year or less, Estimated Fair Value	29,929,000
Due after one year through five years, Estimated Fair Value	92,978,000
Due after five years through ten years, Estimated Fair Value	119,206,000
Due after ten years, Estimated Fair Value	116,505,000
Mortgage-backed securities, Estimated Fair Value	113,507,000
Total available for sale, Estimated Fair Value	$ 472,124,900	$ 435,149,784