Segment Reporting (Schedule Of Underwriting Results For Operating Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Premiums earned	$ 1,413,640	$ 1,389,998	$ 4,053,115	$ 3,806,805
Incurred losses and LAE	888,097	837,757	2,401,223	2,192,863
Commission and brokerage	300,048	290,519	882,132	820,208
Other underwriting expenses	70,667	63,113	195,282	172,165
Underwriting gain (loss)	154,828	198,609	574,478	621,569
U.S. Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	537,483	640,660	1,464,840	1,573,776
Net written premiums	511,238	615,078	1,383,647	1,536,114
Premiums earned	488,485	559,488	1,480,427	1,478,258
Incurred losses and LAE	225,944	249,004	699,575	701,473
Commission and brokerage	121,050	123,432	364,005	339,166
Other underwriting expenses	13,718	12,118	37,054	33,054
Underwriting gain (loss)	127,773	174,934	379,793	404,565
International [Member]
Segment Reporting Information [Line Items]
Gross written premium	354,871	406,254	966,091	1,181,513
Net written premiums	318,478	352,608	896,872	977,235
Premiums earned	291,396	320,020	935,228	958,399
Incurred losses and LAE	229,013	236,559	630,752	604,166
Commission and brokerage	70,894	73,143	226,321	215,716
Other underwriting expenses	9,128	8,758	25,292	24,683
Underwriting gain (loss)	(17,639)	1,560	52,863	113,834
Bermuda [Member]
Segment Reporting Information [Line Items]
Gross written premium	267,035	205,342	605,365	573,793
Net written premiums	251,678	189,447	557,453	548,210
Premiums earned	222,240	181,754	616,241	546,699
Incurred losses and LAE	154,327	108,961	372,572	310,602
Commission and brokerage	52,980	48,421	151,356	140,968
Other underwriting expenses	9,457	9,360	27,045	25,805
Underwriting gain (loss)	5,476	15,012	65,268	69,324
U.S Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	489,124	364,111	1,173,012	911,242
Net written premiums	418,960	310,690	1,022,389	802,431
Premiums earned	360,742	290,518	888,711	742,038
Incurred losses and LAE	262,328	239,823	662,052	557,047
Commission and brokerage	50,268	40,418	127,125	114,535
Other underwriting expenses	35,677	31,311	99,232	83,672
Underwriting gain (loss)	12,469	(21,034)	302	(13,216)
Mt. Logan Re [Member]
Segment Reporting Information [Line Items]
Gross written premium	72,200	50,334	183,694	109,163
Net written premiums	60,903	49,757	153,281	98,666
Premiums earned	50,777	38,218	132,508	81,411
Incurred losses and LAE	16,485	3,410	36,272	19,575
Commission and brokerage	4,856	5,105	13,325	9,823
Other underwriting expenses	2,687	1,566	6,659	4,951
Underwriting gain (loss)	$ 26,749	$ 28,137	$ 76,252	$ 47,062