Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Fixed Maturities, available-for-sale, amortized cost	$ 2,987,492	$ 3,027,408
Equity Securities, cost		224,159
Equity Securities, cost	245,754
Short-Term Investments, available-for-sale, amortized cost	$ 6,707	$ 6,477
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	36,733,000	36,530,000
Treasury Stock, shares	7,023,000	7,023,000