Industry Segments (Financial Information of Company Operating Segments) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Earned Premiums		$ 1,559,793	$ 1,493,041	$ 3,087,128	$ 2,965,054
Investment Income and Funds		129,049	127,583	259,182	251,822
Other Revenues		167,072	169,141	316,815	317,568
Total revenues		1,855,914	1,789,765	3,663,125	3,534,444
Pre-Tax Income (Loss)		158,314	178,187	332,990	346,904
Net Income (Loss)		108,967	123,035	228,477	241,342
Net investment gains		6,315	27,557	13,658	46,601
Net investment gains, net of tax		4,106	17,911	8,878	30,290
Intersegment Eliminations and Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	[1]	0	0	0	0
Investment Income and Funds	[1]	9,522	6,253	16,025	14,367
Other Revenues	[1]	133,154	117,199	248,761	221,007
Total revenues	[1]	142,676	123,452	264,786	235,374
Pre-Tax Income (Loss)	[1]	(48,335)	(59,962)	(108,714)	(118,720)
Net Income (Loss)	[1]	(30,906)	(39,799)	(70,554)	(78,410)
Insurance-Domestic Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		1,399,865	1,351,382	2,775,223	2,662,658
Insurance-Domestic Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums		1,399,865	1,351,382	2,775,223	2,662,658
Investment Income and Funds		100,162	103,264	205,391	202,348
Other Revenues		27,603	24,385	54,396	49,960
Total revenues		1,527,630	1,479,031	3,035,010	2,914,966
Pre-Tax Income (Loss)		183,261	183,470	389,176	371,639
Net Income (Loss)		123,766	126,096	263,036	256,135
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		159,928	141,659	311,905	302,396
Reinsurance-Global Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums		159,928	141,659	311,905	302,396
Investment Income and Funds		19,365	18,066	37,766	35,107
Other Revenues		0	0	0
Total revenues		179,293	159,725	349,671	337,503
Pre-Tax Income (Loss)		17,073	27,122	38,870	47,384
Net Income (Loss)		12,001	18,827	27,117	33,327
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.