Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Jun. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Segment Reporting Information [Line Items]
Earned Premiums	$ 1,328,862		$ 1,186,533		$ 3,843,496		$ 3,433,541
Investment Income and Funds	125,634		116,019		405,300		434,888
Other Revenues	179,628		117,949		463,059		346,524
Total revenues	1,634,124		1,420,501		4,711,855		4,214,953
Pre-Tax Income (Loss)	198,233		133,693		517,162		469,435
Net Income (Loss)	136,974		100,947		369,546		345,103
Net investment gains, before tax	43,869		22,226		96,896		94,003
Net investment gains, net of tax	28,514		14,811		62,982		61,743
Intersegment Eliminations and Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	0		0		0	[1]	0	[1]
Investment Income and Funds	291		1,894		3,831	[1]	9,358	[1]
Other Revenues	109,634		69,515		285,650	[1]	175,400	[1]
Total revenues	109,925	[1]	71,409	[1]	289,481	[1]	184,758	[1]
Pre-Tax Income (Loss)	(58,501)		(57,885)		(183,941)	[1]	(174,868)	[1]
Net Income (Loss)	(38,248)		(35,945)		(114,674)	[1]	(112,122)	[1]
Insurance-Domestic Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	958,994		873,835		2,769,369		2,530,638
Insurance-Domestic Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums	958,994		873,835		2,769,369		2,530,638
Investment Income and Funds	94,071		82,565		299,430		315,307
Other Revenues	26,125		26,208		80,513		77,121
Total revenues	1,079,190		982,608		3,149,312		2,923,066
Pre-Tax Income (Loss)	172,177		132,498		465,861		424,873
Net Income (Loss)	118,183		94,852		324,069		304,167
Insurance-International Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	189,054		157,773		540,365		456,159
Insurance-International Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums	189,054		157,773		540,365		456,159
Investment Income and Funds	11,151		10,411		36,383		31,936
Other Revenues	0		0		0		0
Total revenues	200,205		168,184		576,748		488,095
Pre-Tax Income (Loss)	16,129		13,806		51,094		43,287
Net Income (Loss)	11,225		10,027		35,794		30,972
Reinsurance-Global Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	180,814		154,925		533,762		446,744
Reinsurance-Global Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums	180,814		154,925		533,762		446,744
Investment Income and Funds	20,121		21,149		65,656		78,287
Other Revenues	0		0		0		0
Total revenues	200,935		176,074		599,418		525,031
Pre-Tax Income (Loss)	24,559		23,048		87,252		82,140
Net Income (Loss)	$ 17,300		$ 17,202		$ 61,375		$ 60,343

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