Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	$ 716,856	$ 664,371
Fixed maturity securities-held-to-maturity	698,513	639,631
Fixed maturity securities-available-for-sale	344,659	331,242
Equity securities	28	28
Short-term investments	6,826	33,684
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	698,513	639,631
Fixed maturity securities-available-for-sale	344,659	331,242
Equity securities	28	28
Cash and cash equivalents	61,589	90,956
Short-term investments	6,826	33,684
Other investments	11,695	11,748
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	716,856	664,371
Fixed maturity securities-available-for-sale	344,659	331,242
Equity securities	28	28
Cash and cash equivalents	61,589	90,956
Short-term investments	6,826	33,684
Other investments	$ 11,695	$ 11,748