Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	$ 643,324	$ 662,276
Fixed maturity securities-held-to-maturity	620,165	645,164
Fixed maturity securities-available-for-sale	460,697	380,022
Equity securities	32	31
Short-term investments	17,165	7,718
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	620,165	645,164
Fixed maturity securities-available-for-sale	460,697	380,022
Equity securities	32	31
Cash and cash equivalents	70,155	69,481
Short-term investments	17,165	7,718
Other investments	10,850	12,217
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	643,324	662,276
Fixed maturity securities-available-for-sale	460,697	380,022
Equity securities	32	31
Cash and cash equivalents	70,155	69,481
Short-term investments	17,165	7,718
Other investments	$ 10,850	$ 12,217