Fair Value Measurements - Schedule of Assets and Liabilities Measured at Amortized Cost (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	$ 561,179	$ 627,349
States and political subdivisions [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	399,155	431,968
Corporate bonds [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	68,243	84,377
Commercial mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	54,244	57,962
U.S. agency-based mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	23,565	36,042
US Treasury Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	6,602	6,174
Obligations of the U.S. Government agencies [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	5,914	6,581
Asset-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	3,456	4,245
Fair Value, Inputs, Level 1 [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	6,602	6,174
Fair Value, Inputs, Level 1 [Member] | States and political subdivisions [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 1 [Member] | Corporate bonds [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 1 [Member] | Commercial mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 1 [Member] | U.S. agency-based mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	6,602	6,174
Fair Value, Inputs, Level 1 [Member] | Obligations of the U.S. Government agencies [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 1 [Member] | Asset-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	554,577	621,175
Fair Value, Inputs, Level 2 [Member] | States and political subdivisions [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	399,155	431,968
Fair Value, Inputs, Level 2 [Member] | Corporate bonds [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	68,243	84,377
Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	54,244	57,962
Fair Value, Inputs, Level 2 [Member] | U.S. agency-based mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	23,565	36,042
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 2 [Member] | Obligations of the U.S. Government agencies [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	5,914	6,581
Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	3,456	4,245
Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | States and political subdivisions [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | Corporate bonds [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | Commercial mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | U.S. agency-based mortgage-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | US Treasury Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | Obligations of the U.S. Government agencies [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value
Fair Value, Inputs, Level 3 [Member] | Asset-backed securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value