Industry Segments (Financial Information of Company Operating Segments) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Earned Premiums		$ 1,570,042	$ 1,527,335
Investment Income and Funds		148,858	130,133
Other Revenues		151,518	149,743
Total revenues		1,870,418	1,807,211
Pre-Tax Income (Loss)		184,297	174,676
Net Income (Loss)		123,447	119,511
Net investment gains		52,348	7,343
Net investment gains, net of tax		34,026	4,773
Intersegment Eliminations and Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums	[1]	0	0
Investment Income and Funds	[1]	12,171	6,503
Other Revenues	[1]	80,883	115,607
Total revenues	[1]	93,054	122,110
Pre-Tax Income (Loss)	[1]	(72,639)	(60,379)
Net Income (Loss)	[1]	(47,773)	(39,649)
Insurance-Domestic Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		1,413,170	1,366,605
Insurance-Domestic Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums		1,413,170	1,366,605
Investment Income and Funds		111,909	99,860
Other Revenues		18,287	26,793
Total revenues		1,543,366	1,493,258
Pre-Tax Income (Loss)		199,994	199,651
Net Income (Loss)		134,095	134,778
Reinsurance-Global Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		156,872	160,730
Reinsurance-Global Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned Premiums		156,872	160,730
Investment Income and Funds		24,778	23,770
Other Revenues		0	0
Total revenues		181,650	184,500
Pre-Tax Income (Loss)		4,594	28,061
Net Income (Loss)		3,099	19,609
Net Investment Gains Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums		0	0
Investment Income and Funds		$ 0	$ 0

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