Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $) In Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Earned Premiums	$ 1,055,823		$ 967,297		$ 3,055,564		$ 2,845,986
Investment Income and Funds	114,063		119,143		409,261		392,435
Other Revenues	109,845		89,672		320,206		254,306
Total revenues	1,279,731		1,176,112		3,785,031		3,492,727
Pre-Tax Income (Loss)	97,445		121,300		368,264		427,714
Net Income (Loss)	77,308		93,619		276,877		322,436
Specialty Segment [Member]
Earned Premiums	367,417		326,239		1,047,567		955,705
Investment Income and Funds	37,438		40,814		138,868		133,027
Other Revenues	664		765		2,065		2,383
Total revenues	405,519		367,818		1,188,500		1,091,115
Pre-Tax Income (Loss)	71,046		61,989		238,979		212,836
Net Income (Loss)	51,502		45,268		171,806		154,559
Regional Segment [Member]
Earned Premiums	267,142		268,089		795,423		798,387
Investment Income and Funds	16,099		18,413		59,459		60,995
Other Revenues	1,207		782		3,377		2,448
Total revenues	284,448		287,284		858,259		861,830
Pre-Tax Income (Loss)	(10,700)		22,946		(1,381)		90,415
Net Income (Loss)	(4,669)		17,159		6,154		66,205
Alternative Markets Segment [Member]
Earned Premiums	156,820		148,830		454,156		458,842
Investment Income and Funds	25,931		28,136		96,072		90,658
Other Revenues	20,408		20,631		64,049		59,228
Total revenues	203,159		197,597		614,277		608,728
Pre-Tax Income (Loss)	33,076		42,007		116,285		138,563
Net Income (Loss)	25,185		30,734		86,979		101,117
Reinsurance Segment [Member]
Earned Premiums	103,906		103,126		315,220		308,316
Investment Income and Funds	18,641		19,779		72,230		75,210
Other Revenues	0		0		0		0
Total revenues	122,547		122,905		387,450		383,526
Pre-Tax Income (Loss)	16,134		26,508		66,857		91,085
Net Income (Loss)	13,165		19,641		52,024		68,373
International Segment [Member]
Earned Premiums	160,538		121,013		443,198		324,736
Investment Income and Funds	10,741		8,722		32,692		25,105
Other Revenues	0		0		0		0
Total revenues	171,279		129,735		475,890		349,841
Pre-Tax Income (Loss)	14,182		12,712		28,208		19,671
Net Income (Loss)	9,874		8,217		18,925		13,631
Corporate, Other and Eliminations Segment [Member]
Earned Premiums	0	[1]	0	[1]	0	[1]	0	[1]
Investment Income and Funds	5,213	[1]	3,279	[1]	9,940	[1]	7,440	[1]
Other Revenues	66,328	[1]	62,290	[1]	177,303	[1]	167,597	[1]
Total revenues	71,541	[1]	65,569	[1]	187,243	[1]	175,037	[1]
Pre-Tax Income (Loss)	(47,531)	[1]	(50,066)	[1]	(154,096)	[1]	(147,506)	[1]
Net Income (Loss)	(31,533)	[1]	(30,764)	[1]	(105,921)	[1]	(96,105)	[1]
Net Investment Gains Segment [Member]
Earned Premiums	0		0		0		0
Investment Income and Funds	0		0		0		0
Other Revenues	21,238		5,204		73,412		22,650
Total revenues	21,238		5,204		73,412		22,650
Pre-Tax Income (Loss)	21,238		5,204		73,412		22,650
Net Income (Loss)	$ 13,784		$ 3,364		$ 46,910		$ 14,656

[1] orate and eliminations represent corporate revenues and expenses, net investment gains and losses and other items that are not allocated to business segments.Ne