Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Information by business segment
Net earned premium	$ 556,668	$ 563,650	$ 1,679,210	$ 1,676,122
Other revenue	79,809	68,023	221,064	197,362
Total revenue	636,477	631,673	1,900,274	1,873,484
Loss and LAE	320,376	304,014	992,547	969,767
Other expense	176,001	174,040	491,400	498,819
Segment Expense	496,377	478,054	1,483,947	1,468,586
Segment Pre Tax Earnings (Loss)	140,100	153,619	416,327	404,898
U.S. Property & Casualty [Member]
Information by business segment
Net earned premium	91,684	87,741	276,647	265,593
Other revenue	4,769	8,415	16,198	15,300
Total revenue	96,453	96,156	292,845	280,893
Loss and LAE	13,666	53,229	121,060	154,156
Other expense	32,044	29,581	84,801	89,348
Segment Expense	45,710	82,810	205,861	243,504
Segment Pre Tax Earnings (Loss)	50,743	13,346	86,984	37,389
Professional Liability [Member]
Information by business segment
Net earned premium	92,439	97,549	277,662	298,454
Other revenue	(21)	532	304	799
Total revenue	92,418	98,081	277,966	299,253
Loss and LAE	30,100	36,183	141,921	170,506
Other expense	10,909	13,414	46,781	49,621
Segment Expense	41,009	49,597	188,702	220,127
Segment Pre Tax Earnings (Loss)	51,409	48,484	89,264	79,126
Accident & Health [Member]
Information by business segment
Net earned premium	223,048	209,049	657,995	624,077
Other revenue	1,406	1,095	3,736	3,589
Total revenue	224,454	210,144	661,731	627,666
Loss and LAE	163,143	140,344	483,709	447,262
Other expense	33,705	32,025	97,414	93,127
Segment Expense	196,848	172,369	581,123	540,389
Segment Pre Tax Earnings (Loss)	27,606	37,775	80,608	87,277
U.S. Surety & Credit [Member]
Information by business segment
Net earned premium	47,442	53,388	144,673	154,232
Other revenue	406	244	1,027	659
Total revenue	47,848	53,632	145,700	154,891
Loss and LAE	13,436	15,721	32,287	42,444
Other expense	26,501	27,879	80,182	83,402
Segment Expense	39,937	43,600	112,469	125,846
Segment Pre Tax Earnings (Loss)	7,911	10,032	33,231	29,045
International [Member]
Information by business segment
Net earned premium	100,849	105,831	311,261	302,303
Other revenue	888	631	2,790	2,766
Total revenue	101,737	106,462	314,051	305,069
Loss and LAE	99,221	46,924	204,137	126,547
Other expense	42,613	39,253	114,534	108,018
Segment Expense	141,834	86,177	318,671	234,565
Segment Pre Tax Earnings (Loss)	(40,097)	20,285	(4,620)	70,504
Investing [Member]
Information by business segment
Net earned premium	0	0	0	0
Other revenue	72,130	57,183	196,756	174,133
Total revenue	72,130	57,183	196,756	174,133
Loss and LAE	0	0	0	0
Other expense	0	0	0	0
Segment Expense	0	0	0	0
Segment Pre Tax Earnings (Loss)	72,130	57,183	196,756	174,133
Corporate & Other [Member]
Information by business segment
Net earned premium	1,206	10,092	10,972	31,463
Other revenue	231	(77)	253	116
Total revenue	1,437	10,015	11,225	31,579
Loss and LAE	810	11,613	9,433	28,852
Other expense	30,229	31,888	67,688	75,303
Segment Expense	31,039	43,501	77,121	104,155
Segment Pre Tax Earnings (Loss)	$ (29,602)	$ (33,486)	$ (65,896)	$ (72,576)