Schedule - Parent Corporation Financial Statements (Balance Sheets) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assets Abstract
Fixed maturity securities, held-to-maturity - at carrying value (fair value: $811 - 2010)	$ 712,348	$ 1,214,324
Fixed maturity securities, available-for-sale - at fair value (amortized cost: $19,452 - 2011	2,897,373	2,342,742
Short-term investments	217,044	161,155
Cash	762	645	811	3,606
Current federal income tax	731	11,200
Deferred federal income tax	92,686	93,234
Other assets	52,227	61,529
Total assets	5,736,369	5,231,772
Liabilities And Stockholders Equity
Notes payable	307,360	262,333
Other liabilities	148,569	143,743
Total liabilities	4,627,141	4,160,663
Stockholders' Equity:
Preferred stock of $0 par value per share: Authorized shares: 5,000,000; no shares issued or outstanding	0	0
Common stock of $2 par value per share Authorized shares: 360,000,000 Issued: 97,246,711 - 2011; 96,362,667 - 2010	194,494	192,725
Additional paid-in capital	257,370	244,613
Retained earnings	1,167,219	1,176,155
Accumulated other comprehensive income (loss), net of tax	42,294	7,024	(12,460)
Treasury stock - at cost (shares: 42,836,201 - 2011; 42,686,204 - 2010)	(552,149)	(549,408)
Stockholders' Equity	1,109,228	1,071,109	1,002,375
Total liabilities and stockholders' equity	5,736,369	5,231,772
Fixed maturity securities, held-to-maturity, fair value	758,043	1,256,294
Available-for-sale Securities, Amortized Cost	2,766,856	2,285,988
Preferred stock, par value per share	$ 0	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000	5,000,000
Preferred stock, shares issued	0	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	97,246,711	96,362,667
Treasury stock, shares	42,836,201	42,686,204
Parent Company [Member]
Assets Abstract
Fixed maturity securities, held-to-maturity - at carrying value (fair value: $811 - 2010)	0	796
Fixed maturity securities, available-for-sale - at fair value (amortized cost: $19,452 - 2011	19,768	0
Short-term investments	33,948	50,109
Cash	722	605	77	0
Investment in subsidiaries	1,388,970	1,320,886
Current federal income tax	13,030	12,932
Deferred federal income tax	10,590	11,158
Other assets	12,823	11,961
Total assets	1,479,851	1,408,447
Liabilities And Stockholders Equity
Notes payable	249,360	249,333
Intercompany notes payable	107,131	74,785
Other liabilities	14,132	13,220
Total liabilities	370,623	337,338
Stockholders' Equity:
Preferred stock of $0 par value per share: Authorized shares: 5,000,000; no shares issued or outstanding	0	0
Common stock of $2 par value per share Authorized shares: 360,000,000 Issued: 97,246,711 - 2011; 96,362,667 - 2010	194,494	192,725
Additional paid-in capital	257,370	244,613
Retained earnings	1,167,219	1,176,155
Accumulated other comprehensive income (loss), net of tax	42,294	7,024
Treasury stock - at cost (shares: 42,836,201 - 2011; 42,686,204 - 2010)	(552,149)	(549,408)
Stockholders' Equity	1,109,228	1,071,109
Total liabilities and stockholders' equity	1,479,851	1,408,447
Fixed maturity securities, held-to-maturity, fair value		811
Available-for-sale Securities, Amortized Cost	$ 19,542
Preferred stock, par value per share	$ 0
Preferred stock, shares authorized	5,000,000
Common stock, par value per share	$ 2
Common stock, shares authorized	360,000,000
Common stock, shares issued	97,246,711	96,362,667
Treasury stock, shares	42,836,201	42,686,204

Including current and noncurrent portions, aggregate carrying amount of intercompany long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

No definition available.