Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Fixed maturity securities, fair value	$ 610,151	$ 568,931
Fixed maturity securities, cost	462,892	479,871
Equity securities, cost	$ 7,499	$ 0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	20,502,273	20,488,385
Common stock, shares outstanding	19,244,023	19,230,135
Treasury stock, shares	1,258,250	1,258,250