Investments - Gross Unrealized Gains and Losses and Cost or Amortized Cost and Fair Value of Investments Classified as Available-for-sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investment [Line Items]
Cost or Amortized Cost	$ 229,184	$ 151,514
Gross Unrealized Gains	3,036	6,101
Gross Unrealized Losses	(6,988)	(1,710)
Fair Value	225,232	155,905
States and political subdivisions [Member]
Investment [Line Items]
Cost or Amortized Cost	133,239	93,362
Gross Unrealized Gains	1,694	5,022
Gross Unrealized Losses	(4,375)	(142)
Fair Value	130,558	98,242
Corporate bonds [Member]
Investment [Line Items]
Cost or Amortized Cost	63,876	39,211
Gross Unrealized Gains	471	623
Gross Unrealized Losses	(245)	(24)
Fair Value	64,102	39,810
U.S. agency-based mortgage-backed securities [Member]
Investment [Line Items]
Cost or Amortized Cost	10,082	11,941
Gross Unrealized Gains		5
Gross Unrealized Losses	(2,041)	(859)
Fair Value	8,041	11,087
Total fixed maturity [Member]
Investment [Line Items]
Cost or Amortized Cost	207,197	144,514
Gross Unrealized Gains	2,165	5,650
Gross Unrealized Losses	(6,661)	(1,025)
Fair Value	202,701	149,139
Other Investments [Member]
Investment [Line Items]
Cost or Amortized Cost	10,000
Gross Unrealized Gains	271
Gross Unrealized Losses
Fair Value	10,271
Equity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	11,987	7,000
Gross Unrealized Gains	600	451
Gross Unrealized Losses	(327)	(685)
Fair Value	$ 12,260	$ 6,766