Industry Segments (Financial Information of Company Operating Segments) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Earned Premiums		$ 1,585,944	$ 1,531,558	$ 4,673,072	$ 4,496,612
Investment Income and Funds		145,668	133,214	404,850	385,036
Other Revenues		288,115	196,185	604,618	513,753
Total revenues		2,019,727	1,860,957	5,682,540	5,395,401
Pre-Tax Income (Loss)		331,615	228,920	664,605	575,824
Net Income (Loss)		220,650	152,607	449,127	393,949
Net investment gains		175,736	53,904	189,394	100,505
Net investment gains, net of tax		114,228	35,038	123,106	65,328
Intersegment Eliminations and Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	[1]	0	0	0	0
Investment Income and Funds	[1]	6,802	6,757	22,827	21,124
Other Revenues	[1]	89,560	119,260	338,009	340,267
Total revenues	[1]	96,362	126,017	360,836	361,391
Pre-Tax Income (Loss)	[1]	(81,941)	(51,506)		(170,226)
Net Income (Loss)	[1]	(53,055)	(37,684)	(123,610)	(116,094)
Insurance-Domestic Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		1,431,664	1,379,501	4,206,887	4,042,159
Insurance-Domestic Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums		1,431,664	1,379,501	4,206,887	4,042,159
Investment Income and Funds		117,388	106,989	322,779	309,337
Other Revenues		22,819	23,021	77,215	72,981
Total revenues		1,571,871	1,509,511	4,606,881	4,424,477
Pre-Tax Income (Loss)		215,649	204,109	604,825	575,748
Net Income (Loss)		144,310	139,446	407,346	395,581
Insurance-International Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Other Revenues					0
Reinsurance-Global Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		154,280	152,057	466,185	454,453
Reinsurance-Global Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums		154,280	152,057	466,185	454,453
Investment Income and Funds		21,478	19,468	59,244	54,575
Other Revenues		0	0	0
Total revenues		175,758	171,525	525,429	509,028
Pre-Tax Income (Loss)		22,171	22,413	61,041	69,797
Net Income (Loss)		15,167	15,807	42,285	49,134
Corporate, Other and Eliminations Segment [Member] | Intersegment Eliminations and Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Pre-Tax Income (Loss)	[1]			(190,655)
Net Investment Gains Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		0	0	0
Investment Income and Funds		$ 0	$ 0	$ 0	$ 0

[1] Corporate, other and eliminations represent corporate revenues and expenses that are not allocated to business segments.