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
Information by business segment
Net earned premium	$ 563,650	$ 544,256	$ 1,676,122	$ 1,576,987
Other revenue	68,023	66,268	197,362	182,097
Total revenue	631,673	610,524	1,873,484	1,759,084
Loss and LAE	304,014	380,372	969,767	1,062,240
Other expense	174,040	147,360	498,819	454,268
Segment Expense	478,054	527,732	1,468,586	1,516,508
Segment Pre Tax Earnings Loss	153,619	82,792	404,898	242,576
United States Property And Casualty [Member]
Information by business segment
Net earned premium	87,741	85,946	265,593	245,121
Other revenue	8,415	6,890	15,300	16,556
Total revenue	96,156	92,836	280,893	261,677
Loss and LAE	53,229	56,355	154,156	148,783
Other expense	29,581	26,627	89,348	82,202
Segment Expense	82,810	82,982	243,504	230,985
Segment Pre Tax Earnings Loss	13,346	9,854	37,389	30,692
Professional Liability [Member]
Information by business segment
Net earned premium	97,549	104,066	298,454	307,240
Other revenue	532	109	799	358
Total revenue	98,081	104,175	299,253	307,598
Loss and LAE	36,183	119,617	170,506	257,632
Other expense	13,414	6,023	49,621	40,055
Segment Expense	49,597	125,640	220,127	297,687
Segment Pre Tax Earnings Loss	48,484	(21,465)	79,126	9,911
Accident And Health [Member]
Information by business segment
Net earned premium	209,049	191,715	624,077	568,318
Other revenue	1,095	1,275	3,589	3,468
Total revenue	210,144	192,990	627,666	571,786
Loss and LAE	140,344	138,566	447,262	411,851
Other expense	32,025	29,897	93,127	89,228
Segment Expense	172,369	168,463	540,389	501,079
Segment Pre Tax Earnings Loss	37,775	24,527	87,277	70,707
United States Surety And Credit [Member]
Information by business segment
Net earned premium	53,388	51,906	154,232	153,309
Other revenue	244	254	659	955
Total revenue	53,632	52,160	154,891	154,264
Loss and LAE	15,721	12,664	42,444	42,351
Other expense	27,879	27,657	83,402	82,909
Segment Expense	43,600	40,321	125,846	125,260
Segment Pre Tax Earnings Loss	10,032	11,839	29,045	29,004
International [Member]
Information by business segment
Net earned premium	105,831	99,294	302,303	267,458
Other revenue	631	889	2,766	2,791
Total revenue	106,462	100,183	305,069	270,249
Loss and LAE	46,924	45,242	126,547	175,635
Other expense	39,253	35,734	108,018	99,754
Segment Expense	86,177	80,976	234,565	275,389
Segment Pre Tax Earnings Loss	20,285	19,207	70,504	(5,140)
Investing [Member]
Information by business segment
Net earned premium	0	0	0	0
Other revenue	57,183	57,439	174,133	158,472
Total revenue	57,183	57,439	174,133	158,472
Loss and LAE	0	0	0	0
Other expense	0	0	0	0
Segment Expense	0	0	0	0
Segment Pre Tax Earnings Loss	57,183	57,439	174,133	158,472
CorporateAndOther
Information by business segment
Net earned premium	10,092	11,329	31,463	35,541
Other revenue	(77)	(588)	116	(503)
Total revenue	10,015	10,741	31,579	35,038
Loss and LAE	11,613	7,928	28,852	25,988
Other expense	31,888	21,422	75,303	60,120
Segment Expense	43,501	29,350	104,155	86,108
Segment Pre Tax Earnings Loss	$ (33,486)	$ (18,609)	$ (72,576)	$ (51,070)