Investments - Summary of Amortized Cost and Estimated Fair Value of Fixed Maturities (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Held to Maturity, at Amortized Cost	$ 34,371,191	$ 42,100,196
Held to Maturity, Gross Unrealized Gains	916,000	1,636,000
Held to Maturity, Gross Unrealized Losses
Total held to maturity, Estimated Fair Value	35,287,000	43,736,000
Available for Sale, Amortized Cost	685,672,000	663,837,000
Available for Sale, Gross Unrealized Gains	18,745,000	40,362,000
Available for Sale, Gross Unrealized Losses	16,473,000	932,000
Available for Sale, Estimated Fair Value	687,944,000	703,267,000
U.S. Treasury securities and obligations of U.S. government corporations and agencies [Member]
Schedule of Equity Method Investments [Line Items]
Held to Maturity, at Amortized Cost		1,000,000
Held to Maturity, Gross Unrealized Gains		12,000
Held to Maturity, Gross Unrealized Losses
Total held to maturity, Estimated Fair Value		1,012,000
Available for Sale, Amortized Cost	88,497,000	70,254,000
Available for Sale, Gross Unrealized Gains	177,000	1,101,000
Available for Sale, Gross Unrealized Losses	3,139,000	44,000
Available for Sale, Estimated Fair Value	85,535,000	71,311,000
Obligations of states and political subdivisions [Member]
Schedule of Equity Method Investments [Line Items]
Held to Maturity, at Amortized Cost	34,256,000	40,909,000
Held to Maturity, Gross Unrealized Gains	909,000	1,609,000
Held to Maturity, Gross Unrealized Losses
Total held to maturity, Estimated Fair Value	35,165,000	42,518,000
Available for Sale, Amortized Cost	399,950,000	385,372,000
Available for Sale, Gross Unrealized Gains	15,733,000	32,221,000
Available for Sale, Gross Unrealized Losses	9,622,000	606,000
Available for Sale, Estimated Fair Value	406,061,000	416,987,000
Corporate securities [Member]
Schedule of Equity Method Investments [Line Items]
Available for Sale, Amortized Cost	66,530,000	73,942,000
Available for Sale, Gross Unrealized Gains	1,583,000	3,523,000
Available for Sale, Gross Unrealized Losses	1,203,000	109,000
Available for Sale, Estimated Fair Value	66,910,000	77,356,000
Residential mortgage-backed securities [Member]
Schedule of Equity Method Investments [Line Items]
Held to Maturity, at Amortized Cost	115,000	191,000
Held to Maturity, Gross Unrealized Gains	7,000	15,000
Held to Maturity, Gross Unrealized Losses
Total held to maturity, Estimated Fair Value	122,000	206,000
Available for Sale, Amortized Cost	121,757,000	125,606,000
Available for Sale, Gross Unrealized Gains	1,116,000	3,316,000
Available for Sale, Gross Unrealized Losses	2,341,000	66,000
Available for Sale, Estimated Fair Value	120,532,000	128,856,000
Fixed maturities [Member]
Schedule of Equity Method Investments [Line Items]
Available for Sale, Amortized Cost	676,734,000	655,174,000
Available for Sale, Gross Unrealized Gains	18,609,000	40,161,000
Available for Sale, Gross Unrealized Losses	16,305,000	825,000
Available for Sale, Estimated Fair Value	679,038,000	694,510,000
Equity securities [Member]
Schedule of Equity Method Investments [Line Items]
Available for Sale, Amortized Cost	8,938,000	8,663,000
Available for Sale, Gross Unrealized Gains	136,000	201,000
Available for Sale, Gross Unrealized Losses	168,000	107,000
Available for Sale, Estimated Fair Value	$ 8,906,000	$ 8,757,000