Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Earned Premiums	$ 1,186,533	$ 1,055,823	$ 3,433,541		$ 3,055,564
Investment Income and Funds	116,019	114,063	434,888		409,261
Other Revenues	117,949	109,845	346,524		320,206
Total revenues	1,420,501	1,279,731	4,214,953		3,785,031
Pre-Tax Income (Loss)	133,693	96,146	469,435		364,368
Net Income (Loss)	100,947	76,410	345,103		274,184
Specialty Segment [Member]
Earned Premiums	420,165	367,417	1,215,417		1,047,567
Investment Income and Funds	36,245	37,438	138,491		138,868
Other Revenues	577	664	1,788		2,065
Total revenues	456,987	405,519	1,355,696		1,188,500
Pre-Tax Income (Loss)	59,846	70,590	204,573		237,613
Net Income (Loss)	42,731	51,206	145,270		170,918
Regional Segment [Member]
Earned Premiums	276,629	267,142	809,072		795,423
Investment Income and Funds	16,174	16,099	60,780		59,459
Other Revenues	1,695	1,207	4,770		3,377
Total revenues	294,498	284,448	874,622		858,259
Pre-Tax Income (Loss)	33,219	(11,163)	79,211		(2,770)
Net Income (Loss)	23,296	(4,969)	56,884		5,251
Alternative Markets Segment [Member]
Earned Premiums	177,041	156,820	506,149		454,156
Investment Income and Funds	30,146	25,931	116,036		96,072
Other Revenues	23,936	20,408	70,563		64,049
Total revenues	231,123	203,159	692,748		614,277
Pre-Tax Income (Loss)	39,433	32,984	141,089		116,007
Net Income (Loss)	28,824	25,124	102,012		86,798
Reinsurance Segment [Member]
Earned Premiums	111,599	103,906	327,452		315,220
Investment Income and Funds	19,112	18,641	70,435		72,230
Other Revenues	0	0	0		0
Total revenues	130,711	122,547	397,887		387,450
Pre-Tax Income (Loss)	21,118	16,109	74,742		66,782
Net Income (Loss)	15,732	13,148	54,837		51,975
International Segment [Member]
Earned Premiums	201,099	160,538	575,451		443,198
Investment Income and Funds	12,448	10,741	39,788		32,692
Other Revenues	0	0	0		0
Total revenues	213,547	171,279	615,239		475,890
Pre-Tax Income (Loss)	15,736	13,919	50,685		27,420
Net Income (Loss)	7,141	9,650	22,553		18,253
Corporate, Other and Eliminations Segment [Member]
Earned Premiums	0	0	0	[1]	0	[1]
Investment Income and Funds	1,894	5,213	9,358	[1]	9,940	[1]
Other Revenues	69,515	66,328	175,400	[1]	177,303	[1]
Total revenues	71,409	71,541	184,758	[1]	187,243	[1]
Pre-Tax Income (Loss)	(57,885)	(47,531)	(174,868)	[1]	(154,096)	[1]
Net Income (Loss)	(31,588)	(31,533)	(98,196)	[1]	(105,921)	[1]
Net Investment Gains Segment [Member]
Earned Premiums	0	0	0		0
Investment Income and Funds	0	0	0		0
Other Revenues	22,226	21,238	94,003		73,412
Total revenues	22,226	21,238	94,003		73,412
Pre-Tax Income (Loss)	22,226	21,238	94,003		73,412
Net Income (Loss)	$ 14,811	$ 13,784	$ 61,743		$ 46,910

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