Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Fixed maturity securities, fair value	$ 615,217	$ 616,772
Fixed maturity securities, cost	464,740	479,772
Equity securities, cost	$ 20,769	$ 19,962
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	20,533,230	20,528,230
Common stock, shares outstanding	19,274,980	19,269,980
Treasury stock, shares	1,258,250	1,258,250