Investments - Gross Unrealized Gains and Losses and Cost and Fair Value of Investments Classified as Available-for-sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Investment [Line Items]
Cost or Amortized Cost	$ 215,468	$ 151,514
Gross Unrealized Gains	2,953	6,101
Gross Unrealized Losses	(5,549)	(1,710)
Securities available for sale/Available-for-sale, Fair Value	212,872	155,905
States and political subdivisions [Member]
Investment [Line Items]
Cost or Amortized Cost	132,603	93,362
Gross Unrealized Gains	2,229	5,022
Gross Unrealized Losses	(2,567)	(142)
Securities available for sale/Available-for-sale, Fair Value	132,265	98,242
Corporate bonds [Member]
Investment [Line Items]
Cost or Amortized Cost	58,566	39,211
Gross Unrealized Gains	377	623
Gross Unrealized Losses	(273)	(24)
Securities available for sale/Available-for-sale, Fair Value	58,670	39,810
U.S. agency-based mortgage-backed securities [Member]
Investment [Line Items]
Cost or Amortized Cost	10,418	11,941
Gross Unrealized Gains	2	5
Gross Unrealized Losses	(1,981)	(859)
Securities available for sale/Available-for-sale, Fair Value	8,439	11,087
Total fixed maturity [Member]
Investment [Line Items]
Cost or Amortized Cost	201,587	144,514
Gross Unrealized Gains	2,608	5,650
Gross Unrealized Losses	(4,821)	(1,025)
Securities available for sale/Available-for-sale, Fair Value	199,374	149,139
Equity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	13,881	7,000
Gross Unrealized Gains	345	451
Gross Unrealized Losses	(728)	(685)
Securities available for sale/Available-for-sale, Fair Value	$ 13,498	$ 6,766