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, 2014	Dec. 31, 2013
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	$ 327,753	$ 263,891
Available-for-Sale, Gross Unrealized Gains	8,445	2,914
Available-for-Sale, Gross Unrealized Losses	(4,094)	(9,035)
Available-for-Sale, Fair Value	332,104	257,770
Total fixed maturity [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	314,307	244,409
Available-for-Sale, Gross Unrealized Gains	6,973	1,936
Available-for-Sale, Gross Unrealized Losses	(4,002)	(8,468)
Available-for-Sale, Fair Value	317,278	237,877
Other investments [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	10,000	10,000
Available-for-Sale, Gross Unrealized Gains	1,228	591
Available-for-Sale, Fair Value	11,228	10,591
States and Political Subdivisions [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	151,839	154,024
Available-for-Sale, Gross Unrealized Gains	6,549	1,491
Available-for-Sale, Gross Unrealized Losses	(1,599)	(5,140)
Available-for-Sale, Fair Value	156,789	150,375
Corporate Bonds [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	152,560	80,344
Available-for-Sale, Gross Unrealized Gains	424	445
Available-for-Sale, Gross Unrealized Losses	(314)	(361)
Available-for-Sale, Fair Value	152,670	80,428
U.S. Agency-Based Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	9,908	10,041
Available-for-Sale, Gross Unrealized Losses	(2,089)	(2,967)
Available-for-Sale, Fair Value	7,819	7,074
Equity securities [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	3,446	9,482
Available-for-Sale, Gross Unrealized Gains	244	387
Available-for-Sale, Gross Unrealized Losses	(92)	(567)
Available-for-Sale, Fair Value	$ 3,598	$ 9,302