Parent Corporation Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
ASSETS
Fixed maturity securities, available-for-sale – at fair value (amortized cost: $55,447 - 2013; $40,701 – 2012)	$ 3,715,536	$ 3,296,013
Short-term investments	174,251	214,479
Cash	193	210	762	645
Current federal income tax	512	2,569
Deferred federal income tax	122,613	119,136
Other assets	75,727	57,661
Total assets	6,270,170	6,794,216
Liabilities:
Notes payable	392,414	307,387
Other liabilities	203,476	200,194
Total liabilities	5,116,242	5,703,624
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: 99,120,235 - 2013; 98,194,224 - 2012	198,240	196,388
Additional paid-in capital	288,182	270,654
Retained earnings	1,202,015	1,125,154
Accumulated other comprehensive income	24,851	54,040
Treasury stock - at cost (shares: 43,198,622 - 2013; 43,030,776 - 2012)	(559,360)	(555,644)
Total stockholders’ equity	1,153,928	1,090,592	1,058,328
Total liabilities and stockholders’ equity	6,270,170	6,794,216
Parent Company [Member]
ASSETS
Fixed maturity securities, available-for-sale – at fair value (amortized cost: $55,447 - 2013; $40,701 – 2012)	55,623	41,202
Short-term investments	15,399	26,787
Cash	193	210	722	605
Investment in subsidiaries	1,493,996	1,356,701
Current federal income tax	28,471	8,133
Deferred federal income tax	15,122	19,840
Other assets	9,410	9,695
Total assets	1,618,214	1,462,568
Liabilities:
Notes payable	334,414	249,387
Intercompany notes payable	102,721	103,443
Other liabilities	27,151	19,146
Total liabilities	464,286	371,976
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: 99,120,235 - 2013; 98,194,224 - 2012	198,240	196,388
Additional paid-in capital	288,182	270,654
Retained earnings	1,202,015	1,125,154
Accumulated other comprehensive income	24,851	54,040
Treasury stock - at cost (shares: 43,198,622 - 2013; 43,030,776 - 2012)	(559,360)	(555,644)
Total stockholders’ equity	1,153,928	1,090,592
Total liabilities and stockholders’ equity	$ 1,618,214	$ 1,462,568