Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Fixed income securities, held-to-maturity, fair value	$ 403,536	$ 416,981
Fixed maturity securities, available-for-sale, amortized cost	3,748,456	3,675,977
Equity securities, available-for-sale, cost	162,370	155,350
Premiums receivable, allowance for uncollectible accounts	3,771	4,442
Property and equipment, accumulated depreciation and amortization	$ 181,959	$ 179,192
Preferred stock, par value per share	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 2	$ 2
Common stock, shares authorized	360,000,000	360,000,000
Common stock, shares issued	99,536,697	99,120,235
Treasury stock, shares	43,317,498	43,198,622