Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Fixed maturity securities, held-to-maturity, fair value	$ 646,035	$ 758,043
Fixed maturity securities, available-for-sale, amortized cost	3,091,740	2,766,856
Equity securities, available-for-sale, cost	127,867	143,826
Premiums receivable, allowance for uncollectible accounts	3,684	3,768
Property and equipment, accumulated depreciation and amortization	$ 167,052	$ 160,294
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	98,014,074	97,246,711
Treasury stock, shares	43,012,714	42,836,201