Schedule II - Condensed Financial Information of Registrant (Balance Sheets (Parent Company)) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets:
Cash and cash equivalents	$ 839,738	$ 905,670	$ 911,742	$ 642,952
Fixed maturity securities available for sale at fair value (cost $61,084 and $281,708 at December 31, 2013 and 2012, respectively)	11,616,844	11,943,956
Equity securities available for sale, at fair value (cost $4,668 in 2013 and $0 in 2012)	283,338	376,022
Deferred Federal income taxes	20,120	0
Current Federal income taxes	24,737	0
Property, furniture and equipment at cost, less accumulated depreciation	339,448	267,227
Other assets	335,225	242,135
Total assets	20,551,796	20,155,896
Liabilities:
Other liabilities	848,749	981,626
Current Federal income taxes		22,546
Deferred Federal income taxes	0	60,255
Junior subordinated debentures	339,800	243,206
Total liabilities	16,182,402	15,820,430
Stockholders' equity:
Preferred stock	0	0
Common stock	47,024	47,024
Additional paid-in capital	967,440	945,166
Retained earnings (including accumulated undistributed net income of subsidiaries of $4,393,420 and $4,023,780 at December 31, 2013 and 2012, respectively)	5,265,015	4,817,807
Accumulated other comprehensive income	189,391	465,631
Treasury stock, at cost	(2,132,835)	(1,969,411)
Total common stockholders’ equity	4,336,035	4,306,217
Total liabilities and equity	20,551,796	20,155,896
Equity securities available for sale at cost	203,627	308,175
Parent Company
Assets:
Cash and cash equivalents	17,315	162,972	270,637	29,476
Fixed maturity securities available for sale at fair value (cost $61,084 and $281,708 at December 31, 2013 and 2012, respectively)	63,115	286,597
Equity securities available for sale, at fair value (cost $4,668 in 2013 and $0 in 2012)	11,240	25,699
Investment in subsidiaries	6,250,979	5,979,539
Due from subsidiaries	13,648	106,334
Deferred Federal income taxes	51,346	0
Current Federal income taxes	17,540	0
Property, furniture and equipment at cost, less accumulated depreciation	9,028	7,895
Other assets	5,795	10,710
Total assets	6,440,006	6,579,746
Liabilities:
Due to subsidiaries	0	0
Other liabilities	148,903	176,416
Current Federal income taxes	0	8,253
Deferred Federal income taxes	0	31,914
Junior subordinated debentures	339,800	243,206
Senior notes	1,615,268	1,813,740
Total liabilities	2,103,971	2,273,529
Stockholders' equity:
Preferred stock	0	0
Common stock	47,024	47,024
Additional paid-in capital	967,440	945,166
Retained earnings (including accumulated undistributed net income of subsidiaries of $4,393,420 and $4,023,780 at December 31, 2013 and 2012, respectively)	5,265,015	4,817,807
Accumulated other comprehensive income	189,391	465,631
Treasury stock, at cost	(2,132,835)	(1,969,411)
Total common stockholders’ equity	4,336,035	4,306,217
Total liabilities and equity	6,440,006	6,579,746
Fixed maturity securities available for sale at cost	61,084	281,708
Equity securities available for sale at cost	4,668	0
Accumulated undistributed net income of subsidiaries	$ 4,393,420	$ 4,023,780