Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Of Financial Instruments [Line Items]
Fixed maturity securities-held-to-maturity	$ 607,512	$ 561,179
Fixed maturity securities-held-to-maturity	579,145	536,583
Fixed maturity securities-available-for-sale	284,613	237,877
Equity securities	3,980	9,302
Carrying Amount [Member]
Fair Value Of Financial Instruments [Line Items]
Fixed maturity securities-held-to-maturity	579,145	536,583
Fixed maturity securities-available-for-sale	284,613	237,877
Equity securities	3,980	9,302
Cash and cash equivalents	98,818	123,077
Short-term investments	85,806	84,422
Other investments	11,092	10,591
Fair Value [Member]
Fair Value Of Financial Instruments [Line Items]
Fixed maturity securities-held-to-maturity	607,512	561,179
Fixed maturity securities-available-for-sale	284,613	237,877
Equity securities	3,980	9,302
Cash and cash equivalents	98,818	123,077
Short-term investments	85,806	84,422
Other investments	$ 11,092	$ 10,591