Consolidated Balance Sheets (Parenthetical) $ in Thousands	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Statement Of Financial Position [Abstract]
Fixed Maturities, available-for-sale, amortized cost | $	$ 2,752,102	$ 2,628,225
Equity Securities, available-for-sale, cost | $	334,739	327,911
Short-Term Investments, amortized cost | $	$ 247,602	$ 143,451
Preferred Stock, par value | $ / shares	$ 0.10	$ 0.10
Preferred Stock, authorized shares	1,000,000	1,000,000
Preferred Stock, issued shares	0	0
Common Stock, par value | $ / shares	$ 0.10	$ 0.10
Common Stock, authorized shares	50,000,000	50,000,000
Common Stock, issued shares	36,526,000	36,147,000
Treasury Stock, shares	7,023,000	7,023,000