Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Fixed maturities, available-for-sale, amortized cost	$ 2,367,172	$ 2,323,959
Equity securities, available-for-sale, cost	265,760	154,843
Short-term investments, amortized cost	$ 233,109	$ 179,527
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	17,926,323	17,792,846
Treasury stock, shares	3,511,380	3,511,380