Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Fixed maturities, available-for-sale, amortized cost	$ 2,558,621	$ 2,400,245
Equity securities, available-for-sale, cost	292,698	281,943
Short-term investments, amortized cost	$ 144,845	$ 217,743
Preferred stock, par value	$ 0.10	$ 0.10
Preferred stock, authorized shares	1,000,000	1,000,000
Preferred stock, issued shares	0	0
Common stock, par value	$ 0.10	$ 0.10
Common stock, authorized shares	50,000,000	50,000,000
Common stock, issued shares	18,055,818	17,942,269
Treasury stock, shares	3,511,380	3,511,380