Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Information by business segment
Net earned premium	$ 561,356	$ 565,331	$ 1,122,542	$ 1,112,472
Other revenue	68,075	66,957	141,255	129,339
Total revenue	629,431	632,288	1,263,797	1,241,811
Loss and LAE	339,474	336,825	672,171	665,753
Other expense	165,126	161,144	315,399	324,779
Segment Expense	504,600	497,969	987,570	990,532
Segment Pre Tax Earnings (Loss)	124,831	134,319	276,227	251,279
U.S. Property & Casualty [Member]
Information by business segment
Net earned premium	91,432	88,834	184,963	177,852
Other revenue	4,245	4,522	11,429	6,885
Total revenue	95,677	93,356	196,392	184,737
Loss and LAE	55,238	51,666	107,394	100,927
Other expense	25,452	30,045	52,757	59,767
Segment Expense	80,690	81,711	160,151	160,694
Segment Pre Tax Earnings (Loss)	14,987	11,645	36,241	24,043
Professional Liability [Member]
Information by business segment
Net earned premium	92,444	99,467	185,223	200,905
Other revenue	739	134	325	267
Total revenue	93,183	99,601	185,548	201,172
Loss and LAE	55,435	65,168	111,821	134,323
Other expense	18,124	18,676	35,872	36,207
Segment Expense	73,559	83,844	147,693	170,530
Segment Pre Tax Earnings (Loss)	19,624	15,757	37,855	30,642
Accident & Health [Member]
Information by business segment
Net earned premium	217,822	208,147	434,947	415,028
Other revenue	1,140	1,157	2,330	2,494
Total revenue	218,962	209,304	437,277	417,522
Loss and LAE	160,139	154,396	320,566	306,918
Other expense	32,583	30,948	63,709	61,102
Segment Expense	192,722	185,344	384,275	368,020
Segment Pre Tax Earnings (Loss)	26,240	23,960	53,002	49,502
U.S. Surety & Credit [Member]
Information by business segment
Net earned premium	50,054	53,115	97,231	100,844
Other revenue	384	200	621	415
Total revenue	50,438	53,315	97,852	101,259
Loss and LAE	5,637	15,690	18,851	26,723
Other expense	27,402	27,403	53,681	55,523
Segment Expense	33,039	43,093	72,532	82,246
Segment Pre Tax Earnings (Loss)	17,399	10,222	25,320	19,013
International [Member]
Information by business segment
Net earned premium	105,270	105,188	210,412	196,472
Other revenue	1,124	941	1,902	2,135
Total revenue	106,394	106,129	212,314	198,607
Loss and LAE	58,997	41,856	104,916	79,623
Other expense	36,212	36,612	71,921	68,765
Segment Expense	95,209	78,468	176,837	148,388
Segment Pre Tax Earnings (Loss)	11,185	27,661	35,477	50,219
Investing [Member]
Information by business segment
Net earned premium	0	0	0	0
Other revenue	60,291	59,769	124,626	116,950
Total revenue	60,291	59,769	124,626	116,950
Loss and LAE	0	0	0	0
Other expense	0	0	0	0
Segment Expense	0	0	0	0
Segment Pre Tax Earnings (Loss)	60,291	59,769	124,626	116,950
Corporate & Other [Member]
Information by business segment
Net earned premium	4,334	10,580	9,766	21,371
Other revenue	152	234	22	193
Total revenue	4,486	10,814	9,788	21,564
Loss and LAE	4,028	8,049	8,623	17,239
Other expense	25,353	17,460	37,459	43,415
Segment Expense	29,381	25,509	46,082	60,654
Segment Pre Tax Earnings (Loss)	$ (24,895)	$ (14,695)	$ (36,294)	$ (39,090)