Fair Values of Financial Instruments - Summary of Carrying or Reported Values and Corresponding Fair Values for Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held to maturity	$ 568,931	$ 662,276
Fixed maturity securities—held to maturity	562,434	645,164
Fixed maturity securities—available for sale	479,097	380,022
Equity securities	33	31
Cash and cash equivalents	58,936	69,481
Short-term investments	29,580	7,718
Other investments	13,330	12,217
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities—held to maturity	562,434	645,164
Fixed maturity securities—available for sale	479,097	380,022
Equity securities	33	31
Cash and cash equivalents	58,936	69,481
Short-term investments	29,580	7,718
Other investments	$ 13,330	$ 12,217