Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value Of Financial Instruments [Line Items]
Fixed maturity securities-held-to-maturity	$ 575,175	$ 561,179
Fixed maturity securities-held-to-maturity	548,612	536,583
Fixed maturity securities-available-for-sale	268,189	237,877
Equity securities	3,682	9,302
Carrying Amount [Member]
Fair Value Of Financial Instruments [Line Items]
Fixed maturity securities-held-to-maturity	548,612	536,583
Fixed maturity securities-available-for-sale	268,189	237,877
Equity securities	3,682	9,302
Cash and cash equivalents	106,860	123,077
Short-term investments	85,031	84,422
Other investments	10,820	10,591
Fair Value [Member]
Fair Value Of Financial Instruments [Line Items]
Fixed maturity securities-held-to-maturity	575,175	561,179
Fixed maturity securities-available-for-sale	268,189	237,877
Equity securities	3,682	9,302
Cash and cash equivalents	106,860	123,077
Short-term investments	85,031	84,422
Other investments	$ 10,820	$ 10,591