Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Information by business segment
Net earned premium	$ 561,186	$ 547,141
Other revenue	73,180	62,382
Total revenue	634,366	609,523
Loss and LAE	332,697	328,928
Other expense	150,273	163,635
Segment Expense	482,970	492,563
Segment Pre Tax Earnings Loss	151,396	116,960
United States Property And Casualty [Member]
Information by business segment
Net earned premium	93,531	89,018
Other revenue	7,184	2,363
Total revenue	100,715	91,381
Loss and LAE	52,156	49,261
Other expense	27,305	29,722
Segment Expense	79,461	78,983
Segment Pre Tax Earnings Loss	21,254	12,398
Professional Liability [Member]
Information by business segment
Net earned premium	92,779	101,438
Other revenue	(414)	133
Total revenue	92,365	101,571
Loss and LAE	56,386	69,155
Other expense	17,748	17,531
Segment Expense	74,134	86,686
Segment Pre Tax Earnings Loss	18,231	14,885
Accident And Health [Member]
Information by business segment
Net earned premium	217,125	206,881
Other revenue	1,190	1,337
Total revenue	218,315	208,218
Loss and LAE	160,427	152,522
Other expense	31,126	30,154
Segment Expense	191,553	182,676
Segment Pre Tax Earnings Loss	26,762	25,542
United States Surety And Credit [Member]
Information by business segment
Net earned premium	47,177	47,729
Other revenue	237	215
Total revenue	47,414	47,944
Loss and LAE	13,214	11,033
Other expense	26,279	28,120
Segment Expense	39,493	39,153
Segment Pre Tax Earnings Loss	7,921	8,791
International [Member]
Information by business segment
Net earned premium	105,142	91,284
Other revenue	778	1,194
Total revenue	105,920	92,478
Loss and LAE	45,919	37,767
Other expense	35,709	32,153
Segment Expense	81,628	69,920
Segment Pre Tax Earnings Loss	24,292	22,558
Investing [Member]
Information by business segment
Net earned premium	0	0
Other revenue	64,335	57,181
Total revenue	64,335	57,181
Loss and LAE	0	0
Other expense	0	0
Segment Expense	0	0
Segment Pre Tax Earnings Loss	64,335	57,181
Corporate And Other [Member]
Information by business segment
Net earned premium	5,432	10,791
Other revenue	(130)	(41)
Total revenue	5,302	10,750
Loss and LAE	4,595	9,190
Other expense	12,106	25,955
Segment Expense	16,701	35,145
Segment Pre Tax Earnings Loss	$ (11,399)	$ (24,395)