Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	$ 620,781	$ 662,276
Fixed maturity securities-held-to-maturity	601,314	645,164
Fixed maturity securities-available-for-sale	470,620	380,022
Equity securities	32	31
Cash and cash equivalents	86,612	69,481
Short-term investments	11,494	7,718
Other investments	12,174	12,217
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities-held-to-maturity	601,314	645,164
Fixed maturity securities-available-for-sale	470,620	380,022
Equity securities	32	31
Cash and cash equivalents	86,612	69,481
Short-term investments	11,494	7,718
Other investments	$ 12,174	$ 12,217