Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Earned Premiums	$ 1,099,651		$ 982,497
Investment Income and Funds	157,619		146,126
Other Revenues	121,435		105,728
Total revenues	1,378,705		1,234,351
Pre-Tax Income (Loss)	187,303		159,194
Net Income (Loss)	135,318		115,590
Specialty Segment [Member]
Earned Premiums	387,110		330,207
Investment Income and Funds	49,306		50,286
Other Revenues	618		710
Total revenues	437,034		381,203
Pre-Tax Income (Loss)	68,261		89,914
Net Income (Loss)	48,704		63,995
Regional Segment [Member]
Earned Premiums	264,266		261,517
Investment Income and Funds	21,397		21,507
Other Revenues	1,285		1,021
Total revenues	286,948		284,045
Pre-Tax Income (Loss)	31,787		24,435
Net Income (Loss)	22,542		18,257
Alternative Markets Segment [Member]
Earned Premiums	158,693		148,337
Investment Income and Funds	41,383		34,755
Other Revenues	21,974		20,445
Total revenues	222,050		203,537
Pre-Tax Income (Loss)	47,687		41,537
Net Income (Loss)	34,634		30,836
Reinsurance Segment [Member]
Earned Premiums	106,338		105,478
Investment Income and Funds	25,884		27,278
Other Revenues	0		0
Total revenues	132,222		132,756
Pre-Tax Income (Loss)	27,697		25,337
Net Income (Loss)	20,278		19,481
International Segment [Member]
Earned Premiums	183,244		136,958
Investment Income and Funds	13,134		10,558
Other Revenues	0		0
Total revenues	196,378		147,516
Pre-Tax Income (Loss)	19,640		2,253
Net Income (Loss)	9,324		1,861
Corporate, Other and Eliminations Segment [Member]
Earned Premiums	0	[1]	0	[1]
Investment Income and Funds	6,515	[1]	1,742	[1]
Other Revenues	50,067	[1]	54,268	[1]
Total revenues	56,582	[1]	56,010	[1]
Pre-Tax Income (Loss)	(55,260)	[1]	(53,566)	[1]
Net Income (Loss)	(31,246)	[1]	(37,630)	[1]
Net Investment Gains Segment [Member]
Earned Premiums	0		0
Investment Income and Funds	0		0
Other Revenues	47,491		29,284
Total revenues	47,491		29,284
Pre-Tax Income (Loss)	47,491		29,284
Net Income (Loss)	$ 31,082		$ 18,790

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