Segments (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Information by business segment
Net earned premium	$ 544,256,000	$ 516,166,000	$ 1,576,987,000	$ 1,532,138,000
Other revenue	66,268,000	59,782,000	182,097,000	193,235,000
Segment revenue	610,524,000	575,948,000	1,759,084,000	1,725,373,000
Loss and LAE	380,372,000	297,138,000	1,062,240,000	922,645,000
Other expense	147,360,000	146,798,000	454,268,000	447,938,000
Segment expense	(527,732,000)	(443,936,000)	(1,516,508,000)	(1,370,583,000)
Segment pretax earnings (loss)	82,792,000	132,012,000	242,576,000	354,790,000
Decrease in International segment's pretax earnings due to catastrophe losses	29,400,000		101,700,000	15,600,000
Decrease in Professional Liability segment's pretax earnings due to Loss Development	58,100,000		75,100,000
U.S. Property & Casualty [Member]
Information by business segment
Net earned premium	85,946,000	84,802,000	245,121,000	258,427,000
Other revenue	6,890,000	5,033,000	16,556,000	24,128,000
Segment revenue	92,836,000	89,835,000	261,677,000	282,555,000
Loss and LAE	56,355,000	61,883,000	148,783,000	164,684,000
Other expense	26,627,000	21,289,000	82,202,000	75,890,000
Segment expense	(82,982,000)	(83,172,000)	(230,985,000)	(240,574,000)
Segment pretax earnings (loss)	9,854,000	6,663,000	30,692,000	41,981,000
Professional Liability [Member]
Information by business segment
Net earned premium	104,066,000	103,696,000	307,240,000	321,849,000
Other revenue	109,000	20,000	358,000	458,000
Segment revenue	104,175,000	103,716,000	307,598,000	322,307,000
Loss and LAE	119,617,000	63,212,000	257,632,000	196,154,000
Other expense	6,023,000	18,866,000	40,055,000	57,171,000
Segment expense	(125,640,000)	(82,078,000)	(297,687,000)	(253,325,000)
Segment pretax earnings (loss)	(21,465,000)	21,638,000	9,911,000	68,982,000
Accident & Health [Member]
Information by business segment
Net earned premium	202,999,000	193,252,000	603,656,000	567,739,000
Other revenue	1,277,000	1,113,000	3,471,000	2,830,000
Segment revenue	204,276,000	194,365,000	607,127,000	570,569,000
Loss and LAE	147,278,000	138,869,000	438,883,000	412,438,000
Other expense	30,887,000	30,908,000	92,882,000	89,967,000
Segment expense	(178,165,000)	(169,777,000)	(531,765,000)	(502,405,000)
Segment pretax earnings (loss)	26,111,000	24,588,000	75,362,000	68,164,000
U.S. Surety & Credit [Member]
Information by business segment
Net earned premium	51,906,000	49,807,000	153,309,000	148,427,000
Other revenue	254,000	127,000	955,000	455,000
Segment revenue	52,160,000	49,934,000	154,264,000	148,882,000
Loss and LAE	12,664,000	10,296,000	42,351,000	38,157,000
Other expense	27,657,000	28,007,000	82,909,000	81,699,000
Segment expense	(40,321,000)	(38,303,000)	(125,260,000)	(119,856,000)
Segment pretax earnings (loss)	11,839,000	11,631,000	29,004,000	29,026,000
International [Member]
Information by business segment
Net earned premium	99,294,000	84,539,000	267,458,000	234,471,000
Other revenue	889,000	1,466,000	2,791,000	6,177,000
Segment revenue	100,183,000	86,005,000	270,249,000	240,648,000
Loss and LAE	45,242,000	23,227,000	175,635,000	107,601,000
Other expense	35,734,000	29,654,000	99,754,000	89,559,000
Segment expense	(80,976,000)	(52,881,000)	(275,389,000)	(197,160,000)
Segment pretax earnings (loss)	19,207,000	33,124,000	(5,140,000)	43,488,000
Investing [Member]
Information by business segment
Net earned premium	0	0	0	0
Other revenue	57,439,000	51,894,000	158,472,000	158,200,000
Segment revenue	57,439,000	51,894,000	158,472,000	158,200,000
Loss and LAE	0	0	0	0
Other expense	0	0	0	0
Segment expense	0	0	0	0
Segment pretax earnings (loss)	57,439,000	51,894,000	158,472,000	158,200,000
Corporate and Other [Member]
Information by business segment
Net earned premium	45,000	70,000	203,000	1,225,000
Other revenue	(590,000)	129,000	(506,000)	987,000
Segment revenue	(545,000)	199,000	(303,000)	2,212,000
Loss and LAE	(784,000)	(349,000)	(1,044,000)	3,611,000
Other expense	20,432,000	18,074,000	56,466,000	53,652,000
Segment expense	(19,648,000)	(17,725,000)	(55,422,000)	(57,263,000)
Segment pretax earnings (loss)	$ (20,193,000)	$ (17,526,000)	$ (55,725,000)	$ (55,051,000)