Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2011		Jun. 30, 2012
Earned Premiums	$ 1,147,357	$ 1,017,244	$ 1,999,741		$ 2,247,008
Investment Income and Funds	161,250	149,072	295,198		318,869
Other Revenues	107,140	104,633	210,361		228,575
Total revenues	1,415,747	1,270,949	2,505,300		2,794,452
Pre-Tax Income (Loss)	148,439	109,028	268,222		335,742
Net Income (Loss)	108,838	82,184	197,774		244,156
Specialty Segment [Member]
Earned Premiums	408,142	349,943	680,150		795,252
Investment Income and Funds	52,940	51,144	101,430		102,246
Other Revenues	593	691	1,401		1,211
Total revenues	461,675	401,778	782,981		898,709
Pre-Tax Income (Loss)	76,466	77,109	167,023		144,727
Net Income (Loss)	53,835	55,717	119,712		102,539
Regional Segment [Member]
Earned Premiums	268,177	266,764	528,281		532,443
Investment Income and Funds	23,209	21,853	43,360		44,606
Other Revenues	1,790	1,149	2,170		3,075
Total revenues	293,176	289,766	573,811		580,124
Pre-Tax Income (Loss)	14,205	(16,042)	8,393		45,992
Net Income (Loss)	11,046	(8,037)	10,220		33,588
Alternative Markets Segment [Member]
Earned Premiums	170,415	148,999	297,336		329,108
Investment Income and Funds	44,507	35,386	70,141		85,890
Other Revenues	24,653	23,196	43,641		46,627
Total revenues	239,575	207,581	411,118		461,625
Pre-Tax Income (Loss)	53,969	41,486	83,023		101,656
Net Income (Loss)	38,554	30,838	61,674		73,188
Reinsurance Segment [Member]
Earned Premiums	109,515	105,836	211,314		215,853
Investment Income and Funds	25,439	26,311	53,589		51,323
Other Revenues	0	0	0		0
Total revenues	134,954	132,147	264,903		267,176
Pre-Tax Income (Loss)	25,927	25,336	50,673		53,624
Net Income (Loss)	18,827	19,346	38,827		39,105
International Segment [Member]
Earned Premiums	191,108	145,702	282,660		374,352
Investment Income and Funds	14,206	11,393	21,951		27,340
Other Revenues	0	0	0		0
Total revenues	205,314	157,095	304,611		401,692
Pre-Tax Income (Loss)	15,309	11,248	13,501		34,949
Net Income (Loss)	6,088	6,742	8,603		15,412
Corporate, Other and Eliminations Segment [Member]
Earned Premiums	0	0	0	[1]	0	[1]
Investment Income and Funds	949	2,985	4,727	[1]	7,464	[1]
Other Revenues	55,818	56,707	110,975	[1]	105,885	[1]
Total revenues	56,767	59,692	115,702	[1]	113,349	[1]
Pre-Tax Income (Loss)	(61,723)	(52,999)	(106,565)	[1]	(116,983)	[1]
Net Income (Loss)	(35,362)	(36,758)	(74,388)	[1]	(66,608)	[1]
Net Investment Gains Segment [Member]
Earned Premiums	0	0	0		0
Investment Income and Funds	0	0	0		0
Other Revenues	24,286	22,890	52,174		71,777
Total revenues	24,286	22,890	52,174		71,777
Pre-Tax Income (Loss)	24,286	22,890	52,174		71,777
Net Income (Loss)	$ 15,850	$ 14,336	$ 33,126		$ 46,932

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